/// <summary>
/// Signs a PDF or PDF/A document using specified certificate.
/// </summary>
/// <param name="inputFilename">The filename of input PDF document.</param>
/// <param name="outputFilename">The filename of output PDF document.</param>
/// <param name="certificate">The certificate that should be used
/// for signing the input PDF document.</param>
/// <param name="conformance">The conformance of PDF document.</param>
public static void SignDocument(
    string inputFilename,
    string outputFilename,
    Vintasoft.Imaging.Pdf.PdfDocumentConformance conformance,
    System.Security.Cryptography.X509Certificates.X509Certificate2 certificate)
{
    SignDocument(inputFilename, outputFilename, conformance, certificate, false, null);
}

/// <summary>
/// Signs with timestamp a PDF or PDF/A document using specified certificate.
/// </summary>
/// <param name="inputFilename">The filename of input PDF document.</param>
/// <param name="outputFilename">The filename of output PDF document.</param>
/// <param name="certificate">The certificate that should be used
/// for signing the input PDF document.</param>
/// <param name="addCertificateChain">A value indicating whether signing certificate chain must be added to signature.</param>
/// <param name="conformance">The conformance of PDF document.</param>
/// <param name="timestampServerUrl">Timestamp server URL.</param>
public static void SignDocument(
    string inputFilename,
    string outputFilename,
    Vintasoft.Imaging.Pdf.PdfDocumentConformance conformance,
    System.Security.Cryptography.X509Certificates.X509Certificate2 certificate,
    bool addCertificateChain,
    string timestampServerUrl)
{
    Vintasoft.Imaging.Pdf.Processing.PdfDocumentConverter converter = null;

    // if PDF document conformance is specified
    if (conformance != Vintasoft.Imaging.Pdf.PdfDocumentConformance.Undefined)
    {
        // create PDF document converter
        converter = Vintasoft.Imaging.Pdf.Processing.PdfDocumentConverter.Create(conformance);

        // if is PDF/A converter
        Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter pdfAConverter = converter as Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter;
        if (pdfAConverter != null)
        {
            // set ICC profiles
            //pdfAConverter.DefaultCmykIccProfileFilename = "DefaultCMYK.icc";
            //pdfAConverter.DefaultRgbIccProfileFilename = "DefaultRGB.icc";
        }

        // if PDF document converter is not found
        if (converter == null)
        {
            string message = string.Format("Unsupported {0} conformance.", conformance);
            throw new System.ArgumentOutOfRangeException(message);
        }
    }

    // open PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = new Vintasoft.Imaging.Pdf.PdfDocument(inputFilename))
    {
        // add signature
        AddSignature(document, certificate, addCertificateChain, timestampServerUrl, 1);

        // if PDF document cannot be converted
        if (converter == null)
        {
            if (inputFilename == outputFilename)
            {
                // sign PDF document and save changes in PDF document
                document.SaveChanges();
            }
            else
            {
                // sign PDF document and save PDF document to the output file
                document.SaveChanges(outputFilename);
            }
        }
        else
        {
            if (inputFilename != outputFilename)
            {
                Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter pdfAConverter =
                    (Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter)converter;
                pdfAConverter.OutputFilename = outputFilename;
            }

            // sign and convert PDF document
            Vintasoft.Imaging.Processing.ConversionProfileResult conversionResult =
                converter.Convert(document, new Vintasoft.Imaging.Processing.ProcessingState());

            // if conversion falied
            if (!conversionResult.IsSuccessful)
            {
                // throw conversion exception
                throw conversionResult.CreateConversionException();
            }
        }
    }
}

/// <summary>
/// Adds a digital signature to specified PDF document.
/// </summary>
/// <param name="document">The PDF document.</param>
/// <param name="certificate">The certificate that should be added.</param>
/// <param name="timestampServerUrl">Timestamp server URL.</param>
/// <param name="addCertificateChain">A value indicating whether signing certificate chain must be added to signature.</param>
/// <param name="sigNumber">The number of signature field.</param>
private static void AddSignature(
    Vintasoft.Imaging.Pdf.PdfDocument document,
    System.Security.Cryptography.X509Certificates.X509Certificate2 certificate,
    bool addCertificateChain,
    string timestampServerUrl,
    int sigNumber)
{
    // if PDF document does not have interactive form
    if (document.InteractiveForm == null)
    {
        // create the interactive form in document
        document.InteractiveForm = new Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentInteractiveForm(document);
    }

    // specify that document contains signatures
    document.InteractiveForm.SignatureFlags =
        Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentSignatureFlags.SignaturesExist |
        Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentSignatureFlags.AppendOnly;

    // specify that the viewer application must NOT construct appearance streams and
    // appearance properties for widget annotations in the document
    document.InteractiveForm.NeedAppearances = false;

    // get PDF page on which signature will be placed
    Vintasoft.Imaging.Pdf.Tree.PdfPage page = document.Pages[0];

    // calculate the signature field rectangle (field will be placed in the bottom-center of page)
    System.Drawing.RectangleF signatureRect = new System.Drawing.RectangleF();
    signatureRect.Width = page.MediaBox.Width / 5;
    signatureRect.Height = signatureRect.Width / 3;
    signatureRect.X = page.MediaBox.X + (page.MediaBox.Width - signatureRect.Width) / 2;
    signatureRect.Y = page.MediaBox.Y + signatureRect.Height * sigNumber;

    // create parameters for creation of PKCS#7 signature
    Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignatureCreationParams creationParams =
        new Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignatureCreationParams(certificate, addCertificateChain);
    // if timestamp server is specified
    if (!string.IsNullOrEmpty(timestampServerUrl))
    {
        // specify the timestamp authority client
        creationParams.TimestampAuthorityClient = new Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.TimestampAuthorityWebClient(timestampServerUrl);
    }

    // create PKCS#7 signature
    Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature signature = Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature.CreatePkcs7Signature(
         document.Format, creationParams);

    // create signature info
    Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation signatureInfo =
        new Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation(document, signature);
    signatureInfo.SignerName = certificate.GetNameInfo(
        System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, false);
    signatureInfo.Reason = "Test signing";
    signatureInfo.Location = System.Globalization.CultureInfo.CurrentCulture.EnglishName;
    signatureInfo.SigningTime = System.DateTime.Now;

    // create the signature field
    Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField signatureField =
        new Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField(document, string.Format("MySignature{0}", sigNumber), signatureRect);

    // set the signature information
    signatureField.SignatureInfo = signatureInfo;

    // create the signature appearance
    using (Vintasoft.Imaging.Pdf.Drawing.PdfGraphics g = signatureField.CreateAppearanceGraphics())
    {
        // signature text
        string signatureText = string.Format("Digitally signed by\n{0}",
            signatureInfo.SignerName);

        // signature appearance rect
        System.Drawing.RectangleF rect = new System.Drawing.RectangleF(
            System.Drawing.PointF.Empty,
            signatureField.Annotation.Rectangle.Size);

        // draw background
        g.FillRectangle(new Vintasoft.Imaging.Pdf.Drawing.PdfBrush(
            System.Drawing.Color.FromArgb(255, System.Drawing.Color.Lime)), rect);

        // padding
        rect.Inflate(-rect.Height / 10, -rect.Height / 10);

        // create TimesRoman font
        Vintasoft.Imaging.Pdf.Tree.Fonts.PdfFont font = document.FontManager.GetStandardFont(
            Vintasoft.Imaging.Pdf.Tree.Fonts.PdfStandardFontType.TimesRoman);

        // measure font size
        float fontSize = g.MeasureFontSize(signatureText, font, rect.Width, rect.Height);

        // draw signture text
        g.DrawString(
            signatureText,
            font, fontSize, new Vintasoft.Imaging.Pdf.Drawing.PdfBrush(System.Drawing.Color.Black),
            rect, Vintasoft.Imaging.Pdf.Drawing.PdfContentAlignment.Center, false);
    }

    // add signature field to the interactive form of document
    document.InteractiveForm.Fields.Add(signatureField);

    // if PDF page does not have annotations
    if (page.Annotations == null)
        // create an empty annotation collection for page
        page.Annotations = new Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationList(document);
    // add widget annotation of signature field to the annotation collection of page
    page.Annotations.Add(signatureField.Annotation);
}

''' <summary>
''' Signs a PDF or PDF/A document using specified certificate.
''' </summary>
''' <param name="inputFilename">The filename of input PDF document.</param>
''' <param name="outputFilename">The filename of output PDF document.</param>
''' <param name="certificate">The certificate that should be used
''' for signing the input PDF document.</param>
''' <param name="conformance">The conformance of PDF document.</param>
Public Shared Sub SignDocument(inputFilename As String, outputFilename As String, conformance As Vintasoft.Imaging.Pdf.PdfDocumentConformance, certificate As System.Security.Cryptography.X509Certificates.X509Certificate2)
    SignDocument(inputFilename, outputFilename, conformance, certificate, False, Nothing)
End Sub

''' <summary>
''' Signs with timestamp a PDF or PDF/A document using specified certificate.
''' </summary>
''' <param name="inputFilename">The filename of input PDF document.</param>
''' <param name="outputFilename">The filename of output PDF document.</param>
''' <param name="certificate">The certificate that should be used
''' for signing the input PDF document.</param>
''' <param name="addCertificateChain">A value indicating whether signing certificate chain must be added to signature.</param>
''' <param name="conformance">The conformance of PDF document.</param>
''' <param name="timestampServerUrl">Timestamp server URL.</param>
Public Shared Sub SignDocument(inputFilename As String, outputFilename As String, conformance As Vintasoft.Imaging.Pdf.PdfDocumentConformance, certificate As System.Security.Cryptography.X509Certificates.X509Certificate2, addCertificateChain As Boolean, timestampServerUrl As String)
    Dim converter As Vintasoft.Imaging.Pdf.Processing.PdfDocumentConverter = Nothing

    ' if PDF document conformance is specified
    If conformance <> Vintasoft.Imaging.Pdf.PdfDocumentConformance.Undefined Then
        ' create PDF document converter
        converter = Vintasoft.Imaging.Pdf.Processing.PdfDocumentConverter.Create(conformance)

        ' if is PDF/A converter
        Dim pdfAConverter As Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter = TryCast(converter, Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter)
                ' set ICC profiles
                'pdfAConverter.DefaultCmykIccProfileFilename = "DefaultCMYK.icc";
                'pdfAConverter.DefaultRgbIccProfileFilename = "DefaultRGB.icc";
        If pdfAConverter IsNot Nothing Then
        End If

        ' if PDF document converter is not found
        If converter Is Nothing Then
            Dim message As String = String.Format("Unsupported {0} conformance.", conformance)
            Throw New System.ArgumentOutOfRangeException(message)
        End If
    End If

    ' open PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(inputFilename)
        ' add signature
        AddSignature(document, certificate, addCertificateChain, timestampServerUrl, 1)

        ' if PDF document cannot be converted
        If converter Is Nothing Then
            If inputFilename = outputFilename Then
                ' sign PDF document and save changes in PDF document
                document.SaveChanges()
            Else
                ' sign PDF document and save PDF document to the output file
                document.SaveChanges(outputFilename)
            End If
        Else
            If inputFilename <> outputFilename Then
                Dim pdfAConverter As Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter = DirectCast(converter, Vintasoft.Imaging.Pdf.Processing.PdfA.PdfAConverter)
                pdfAConverter.OutputFilename = outputFilename
            End If

            ' sign and convert PDF document
            Dim conversionResult As Vintasoft.Imaging.Processing.ConversionProfileResult = converter.Convert(document, New Vintasoft.Imaging.Processing.ProcessingState())

            ' if conversion falied
            If Not conversionResult.IsSuccessful Then
                ' throw conversion exception
                Throw conversionResult.CreateConversionException()
            End If
        End If
    End Using
End Sub

''' <summary>
''' Adds a digital signature to specified PDF document.
''' </summary>
''' <param name="document">The PDF document.</param>
''' <param name="certificate">The certificate that should be added.</param>
''' <param name="timestampServerUrl">Timestamp server URL.</param>
''' <param name="addCertificateChain">A value indicating whether signing certificate chain must be added to signature.</param>
''' <param name="sigNumber">The number of signature field.</param>
Private Shared Sub AddSignature(document As Vintasoft.Imaging.Pdf.PdfDocument, certificate As System.Security.Cryptography.X509Certificates.X509Certificate2, addCertificateChain As Boolean, timestampServerUrl As String, sigNumber As Integer)
    ' if PDF document does not have interactive form
    If document.InteractiveForm Is Nothing Then
        ' create the interactive form in document
        document.InteractiveForm = New Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentInteractiveForm(document)
    End If

    ' specify that document contains signatures
    document.InteractiveForm.SignatureFlags = Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentSignatureFlags.SignaturesExist Or Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentSignatureFlags.AppendOnly

    ' specify that the viewer application must NOT construct appearance streams and
    ' appearance properties for widget annotations in the document
    document.InteractiveForm.NeedAppearances = False

    ' get PDF page on which signature will be placed
    Dim page As Vintasoft.Imaging.Pdf.Tree.PdfPage = document.Pages(0)

    ' calculate the signature field rectangle (field will be placed in the bottom-center of page)
    Dim signatureRect As New System.Drawing.RectangleF()
    signatureRect.Width = page.MediaBox.Width / 5
    signatureRect.Height = signatureRect.Width / 3
    signatureRect.X = page.MediaBox.X + (page.MediaBox.Width - signatureRect.Width) / 2
    signatureRect.Y = page.MediaBox.Y + signatureRect.Height * sigNumber

    ' create parameters for creation of PKCS#7 signature
    Dim creationParams As New Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignatureCreationParams(certificate, addCertificateChain)
    ' if timestamp server is specified
    If Not String.IsNullOrEmpty(timestampServerUrl) Then
        ' specify the timestamp authority client
        creationParams.TimestampAuthorityClient = New Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.TimestampAuthorityWebClient(timestampServerUrl)
    End If

    ' create PKCS#7 signature
    Dim signature As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature = Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature.CreatePkcs7Signature(document.Format, creationParams)

    ' create signature info
    Dim signatureInfo As New Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation(document, signature)
    signatureInfo.SignerName = certificate.GetNameInfo(System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, False)
    signatureInfo.Reason = "Test signing"
    signatureInfo.Location = System.Globalization.CultureInfo.CurrentCulture.EnglishName
    signatureInfo.SigningTime = System.DateTime.Now

    ' create the signature field
    Dim signatureField As New Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField(document, String.Format("MySignature{0}", sigNumber), signatureRect)

    ' set the signature information
    signatureField.SignatureInfo = signatureInfo

    ' create the signature appearance
    Using g As Vintasoft.Imaging.Pdf.Drawing.PdfGraphics = signatureField.CreateAppearanceGraphics()
        ' signature text
        Dim signatureText As String = String.Format("Digitally signed by" & vbLf & "{0}", signatureInfo.SignerName)

        ' signature appearance rect
        Dim rect As New System.Drawing.RectangleF(System.Drawing.PointF.Empty, signatureField.Annotation.Rectangle.Size)

        ' draw background
        g.FillRectangle(New Vintasoft.Imaging.Pdf.Drawing.PdfBrush(System.Drawing.Color.FromArgb(255, System.Drawing.Color.Lime)), rect)

        ' padding
        rect.Inflate(-rect.Height / 10, -rect.Height / 10)

        ' create TimesRoman font
        Dim font As Vintasoft.Imaging.Pdf.Tree.Fonts.PdfFont = document.FontManager.GetStandardFont(Vintasoft.Imaging.Pdf.Tree.Fonts.PdfStandardFontType.TimesRoman)

        ' measure font size
        Dim fontSize As Single = g.MeasureFontSize(signatureText, font, rect.Width, rect.Height)

        ' draw signture text
        g.DrawString(signatureText, font, fontSize, New Vintasoft.Imaging.Pdf.Drawing.PdfBrush(System.Drawing.Color.Black), rect, Vintasoft.Imaging.Pdf.Drawing.PdfContentAlignment.Center, _
            False)
    End Using

    ' add signature field to the interactive form of document
    document.InteractiveForm.Fields.Add(signatureField)

    ' if PDF page does not have annotations
    If page.Annotations Is Nothing Then
        ' create an empty annotation collection for page
        page.Annotations = New Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationList(document)
    End If
    ' add widget annotation of signature field to the annotation collection of page
    page.Annotations.Add(signatureField.Annotation)
End Sub

/// <summary>
/// Displays and verifies signatures of PDF document.
/// </summary>
/// <param name="pdfFilename">The filename of PDF document.</param>
public static void VerifyDocumentSignatures(string pdfFilename)
{
    // open PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = 
        new Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename))
    {
        // if document does not have interactive form
        if (document.InteractiveForm == null)
        {
            System.Console.WriteLine("Signature fields are not found.");
            return;
        }

        // get an array of signature fields of document
        Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField[] signatureFields =
            document.InteractiveForm.GetSignatureFields();
        // if document does not have signature fields
        if (signatureFields.Length == 0)
        {
            System.Console.WriteLine("Signture fields are not found.");
            return;
        }

        // for each signature field
        for (int i = 0; i < signatureFields.Length; i++)
        {
            // get reference to the signature field
            Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField signatureField = signatureFields[i];
            // print signature field name
            System.Console.WriteLine(string.Format("[{0}]Signaure field: {1}", i + 1, signatureField.FullyQualifiedName));

            // get information about signature
            Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation signatureInfo = signatureField.SignatureInfo;
            // if signature information is empty
            if (signatureInfo == null)
            {
                System.Console.WriteLine("Empty signature field.");
            }
            // if signature information is NOT empty
            else
            {
                // check is document timestamp signature
                if (signatureInfo.IsTimeStamp)
                    System.Console.WriteLine("Signature is a document timestamp signature");

                // print signature filter
                System.Console.WriteLine(string.Format("Filter      : {0} ({1})", signatureInfo.Filter, signatureInfo.SubFilter));
                // print the signer name
                if (signatureInfo.SignerName != null)
                    System.Console.WriteLine(string.Format("Signed by   : {0}", signatureInfo.SignerName));
                // print the signature reason
                if (signatureInfo.Reason != null)
                    System.Console.WriteLine(string.Format("Reason      : {0}", signatureInfo.Reason));
                // print the signature location
                if (signatureInfo.Location != null)
                    System.Console.WriteLine(string.Format("Location    : {0}", signatureInfo.Location));
                // print the signer contact info
                if (signatureInfo.ContactInfo != null)
                    System.Console.WriteLine(string.Format("Contact Info: {0}", signatureInfo.SignerName));
                // print the signing date
                if (signatureInfo.SigningTime != System.DateTime.MinValue)
                    System.Console.WriteLine(string.Format("Signig Date : {0}", signatureInfo.SigningTime.ToString("f")));

                // get PKCS signature
                bool error = false;
                Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature signature = null;
                try
                {
                    signature = signatureInfo.GetSignature();
                }
                catch (System.Exception e)
                {
                    error = true;
                    System.Console.WriteLine("PKCS signature parsing error: {0}", e.Message);
                }
                if (error)
                    continue;

                // print name of signature algorithm
                System.Console.WriteLine(string.Format("Algorithm   : {0}", signature.SignatureAlgorithmName));

                // print information about signature certificate chain
                System.Console.WriteLine("Sign certificate chain:");
                System.Security.Cryptography.X509Certificates.X509Certificate2[] signCertChain = 
                    signature.SigningCertificateChain;
                string padding = "";
                foreach (System.Security.Cryptography.X509Certificates.X509Certificate2 cert in signCertChain)
                {
                    padding += "    ";
                    System.Console.WriteLine("{0}Serial number: {1}", padding, cert.SerialNumber);
                    System.Console.WriteLine("{0}Issuer       : {1}", padding, cert.GetNameInfo(
                        System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, true));
                    System.Console.WriteLine("{0}Subject      : {1}", padding, cert.GetNameInfo(
                        System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, false));
                }


                // verify digital signature
                VerifyDigitalSignature(signatureInfo, signature);
            }
            System.Console.WriteLine();
        }
    }
}

/// <summary>
/// Verifies the digital signature.
/// </summary>
/// <param name="signature">The signature.</param>
/// <param name="signatureInfo">The signature information.</param>
/// <returns><b>true</b> if signature is valid; otherwise, <b>false</b>.</returns>
public static bool VerifyDigitalSignature(
    Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation signatureInfo,
    Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature signature)
{
    System.Console.WriteLine("Verifying signature...");

    bool signatureVerifyResult = false;
    bool embeddedTimestampVerifyResult = false;
    bool certificateVerifyResult = false;
    bool embeddedTimestampCertificateVerifyResult = false;
    bool signatureCoversWholeDocument = false;
    System.Security.Cryptography.X509Certificates.X509Chain certificateChain = null;
    System.Security.Cryptography.X509Certificates.X509Chain timestampCertificateChain = null;


    // verify signature

    try
    {
        // check that signature covers the whole document
        signatureCoversWholeDocument = signatureInfo.SignatureCoversWholeDocument();

        // verify PKCS signature
        signatureVerifyResult = signature.VerifySignature();

        // if signature has embedded timestamp
        if (signature.HasEmbeddedTimeStamp)
        {
            // verify embedded timestamp
            embeddedTimestampVerifyResult = signature.VerifyTimestamp();
        }

        // build and verify certificate chain
        certificateChain = new System.Security.Cryptography.X509Certificates.X509Chain();
        certificateVerifyResult = certificateChain.Build(signature.SigningCertificate);

        // if signature has embedded timestamp
        if (signature.HasEmbeddedTimeStamp)
        {
            // build and verify timestamp certificate chain
            timestampCertificateChain = new System.Security.Cryptography.X509Certificates.X509Chain();
            embeddedTimestampCertificateVerifyResult = certificateChain.Build(signature.TimestampCertificate);
        }

    }
    catch (System.Exception verificationException)
    {
        System.Console.WriteLine("Verification failed: {0}", verificationException.Message);
        return false;
    }

    bool pageContentModified = false;
    string subsequentChangesMessage = "";
    // if PKCS signature verification is passed AND signature does not cover the whole document
    if (signatureVerifyResult && !signatureCoversWholeDocument)
    {
        try
        {
            // if signature has revision info
            if (signatureInfo.SignedRevision != null)
            {
                // check subsequent changes
                using (Vintasoft.Imaging.Pdf.PdfDocumentRevisionComparer documentChanges = signatureInfo.GetDocumentChanges())
                {
                    // check subsequent changes in pages content
                    pageContentModified = documentChanges.HasModifiedPages;

                    // build subsequent changes message
                    if (documentChanges.ChangedPageContents.Count > 0)
                        subsequentChangesMessage += string.Format("{0} page(s) modified; ", documentChanges.ChangedPageContents.Count);
                    if (documentChanges.AddedPages.Count > 0)
                        subsequentChangesMessage += string.Format("{0} page(s) added; ", documentChanges.AddedPages.Count);
                    if (documentChanges.RemovedPages.Count > 0)
                        subsequentChangesMessage += string.Format("{0} page(s) removed; ", documentChanges.RemovedPages.Count);
                    if (documentChanges.RemovedAnnotations.Count > 0)
                        subsequentChangesMessage += string.Format("annotations(s) on {0} page(s) removed; ", documentChanges.RemovedAnnotations.Count);
                    if (documentChanges.RemovedAnnotations.Count > 0)
                        subsequentChangesMessage += string.Format("removed annotation(s) on {0} page(s); ", documentChanges.RemovedAnnotations.Count);
                    if (documentChanges.AddedAnnotations.Count > 0)
                        subsequentChangesMessage += string.Format("added annotation(s) on {0} page(s); ", documentChanges.AddedAnnotations.Count);
                    if (documentChanges.ChangedAnnotations.Count > 0)
                        subsequentChangesMessage += string.Format("changed annotation(s) on {0} page(s); ", documentChanges.ChangedAnnotations.Count);
                    if (documentChanges.MiscellaneousChanges.Count > 0)
                        subsequentChangesMessage += string.Format("miscellaneous changes: {0}; ", documentChanges.MiscellaneousChanges.Count);
                }
            }
        }
        catch (System.Exception verificationException)
        {
            System.Console.WriteLine("Verification failed: {0}", verificationException.Message);
            return false;
        }
    }

    // print signature verification result

    // if PKCS signature verification is failed OR
    // signature does not cover the whole document AND page(s) content is modified
    if (!signatureVerifyResult || (!signatureCoversWholeDocument && pageContentModified))
        System.Console.WriteLine("Signature is INVALID.");
    // if certificate verification is failed
    else if (!certificateVerifyResult || (signature.HasEmbeddedTimeStamp && (!embeddedTimestampCertificateVerifyResult || !embeddedTimestampVerifyResult)))
        System.Console.WriteLine("Signature validity is UNKNOWN.");
    else
        System.Console.WriteLine("Signature is VALID.");


    // print signature verification details

    // if signature verification is successful
    if (signatureVerifyResult)
    {
        // if signature covers the whole document
        if (signatureCoversWholeDocument)
        {
            System.Console.WriteLine("    Signature verification: Document has not been modified since this signature was applied.");
        }
        // if signature does NOT cover the whole document
        else
        {
            if (pageContentModified)
            {
                System.Console.WriteLine("    Signature verification: Document has been modified or corrupted since it was signed.");
                System.Console.WriteLine(string.Format("    Subsequent changes: {0}.", subsequentChangesMessage));
            }
            else if (subsequentChangesMessage != "")
            {
                System.Console.WriteLine("    Signature verification: The revision of the document that was covered by this signature has not been altered; however, there have been subsequent changes to the document.");
                System.Console.WriteLine(string.Format("    Subsequent changes: {0}.", subsequentChangesMessage));
            }
            else
            {
                System.Console.WriteLine("    Signature verification: Document has not been modified since this signature was applied.");
            }
        }
    }
    // if signature verification is NOT successful
    else
    {
        System.Console.WriteLine("    Signature verification: Document has been modified or corrupted since it was signed.");
    }

    // if signature has embedded timestamp
    if (signature.HasEmbeddedTimeStamp)
    {
        if (embeddedTimestampVerifyResult)
            System.Console.WriteLine("    Timestamp verification: Timestamp is valid.");
        else
            System.Console.WriteLine("    Timestamp verification: Timestamp is valid.");
    }


    // print certificate verification details

    // if certificate chain is present
    if (certificateChain != null)
    {
        // if certificate verification is successful
        if (certificateVerifyResult)
        {
            System.Console.WriteLine("    Certificate verification: Signer's certificate is valid.");
        }
        // if certificate verification is NOT successful
        else
        {
            // print certificate verification status
            System.Console.WriteLine("    Certificate verification: Signer's certificate is invalid:");
            foreach (System.Security.Cryptography.X509Certificates.X509ChainStatus status in certificateChain.ChainStatus)
                System.Console.Write(string.Format("        {0}: {1}", status.Status, status.StatusInformation));
        }
    }

    // if timestamp certificate chain is present
    if (timestampCertificateChain != null)
    {
        // if timestamp certificate verification is successful
        if (embeddedTimestampCertificateVerifyResult)
        {
            System.Console.WriteLine("    Timestamp certificate verification: Signer's certificate is valid.");
        }
        // if timestamp certificate verification is NOT successful
        else
        {
            // print certificate verification status
            System.Console.WriteLine("    Timestamp certificate verification: Signer's certificate is invalid:");
            foreach (System.Security.Cryptography.X509Certificates.X509ChainStatus status in timestampCertificateChain.ChainStatus)
                System.Console.Write(string.Format("        {0}: {1}", status.Status, status.StatusInformation));
        }
    }

    // if signature is not verified
    if (!signatureVerifyResult)
        return false;

    // if signature does NOT cover the whole document and page content was modified
    if (!signatureCoversWholeDocument && pageContentModified)
        return false;

    // if signature certificate is NOT verified
    if (!certificateVerifyResult)
        return false;
    
    if (signature.HasEmbeddedTimeStamp)
    {
        // if timestamp is NOT verified
        if (!embeddedTimestampVerifyResult)
            return false;

        // if timestamp certifiacet is NOT verified
        if (!embeddedTimestampCertificateVerifyResult)
            return false;
    }

    // sigature is VALID
    return true;
}

''' <summary>
''' Displays and verifies signatures of PDF document.
''' </summary>
''' <param name="pdfFilename">The filename of PDF document.</param>
Public Shared Sub VerifyDocumentSignatures(pdfFilename As String)
    ' open PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename)
        ' if document does not have interactive form
        If document.InteractiveForm Is Nothing Then
            System.Console.WriteLine("Signature fields are not found.")
            Return
        End If

        ' get an array of signature fields of document
        Dim signatureFields As Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField() = document.InteractiveForm.GetSignatureFields()
        ' if document does not have signature fields
        If signatureFields.Length = 0 Then
            System.Console.WriteLine("Signture fields are not found.")
            Return
        End If

        ' for each signature field
        For i As Integer = 0 To signatureFields.Length - 1
            ' get reference to the signature field
            Dim signatureField As Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField = signatureFields(i)
            ' print signature field name
            System.Console.WriteLine(String.Format("[{0}]Signaure field: {1}", i + 1, signatureField.FullyQualifiedName))

            ' get information about signature
            Dim signatureInfo As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation = signatureField.SignatureInfo
            ' if signature information is empty
            If signatureInfo Is Nothing Then
                System.Console.WriteLine("Empty signature field.")
            Else
                ' if signature information is NOT empty
                ' check is document timestamp signature
                If signatureInfo.IsTimeStamp Then
                    System.Console.WriteLine("Signature is a document timestamp signature")
                End If

                ' print signature filter
                System.Console.WriteLine(String.Format("Filter      : {0} ({1})", signatureInfo.Filter, signatureInfo.SubFilter))
                ' print the signer name
                If signatureInfo.SignerName IsNot Nothing Then
                    System.Console.WriteLine(String.Format("Signed by   : {0}", signatureInfo.SignerName))
                End If
                ' print the signature reason
                If signatureInfo.Reason IsNot Nothing Then
                    System.Console.WriteLine(String.Format("Reason      : {0}", signatureInfo.Reason))
                End If
                ' print the signature location
                If signatureInfo.Location IsNot Nothing Then
                    System.Console.WriteLine(String.Format("Location    : {0}", signatureInfo.Location))
                End If
                ' print the signer contact info
                If signatureInfo.ContactInfo IsNot Nothing Then
                    System.Console.WriteLine(String.Format("Contact Info: {0}", signatureInfo.SignerName))
                End If
                ' print the signing date
                If signatureInfo.SigningTime <> System.DateTime.MinValue Then
                    System.Console.WriteLine(String.Format("Signig Date : {0}", signatureInfo.SigningTime.ToString("f")))
                End If

                ' get PKCS signature
                Dim [error] As Boolean = False
                Dim signature As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature = Nothing
                Try
                    signature = signatureInfo.GetSignature()
                Catch e As System.Exception
                    [error] = True
                    System.Console.WriteLine("PKCS signature parsing error: {0}", e.Message)
                End Try
                If [error] Then
                    Continue For
                End If

                ' print name of signature algorithm
                System.Console.WriteLine(String.Format("Algorithm   : {0}", signature.SignatureAlgorithmName))

                ' print information about signature certificate chain
                System.Console.WriteLine("Sign certificate chain:")
                Dim signCertChain As System.Security.Cryptography.X509Certificates.X509Certificate2() = signature.SigningCertificateChain
                Dim padding As String = ""
                For Each cert As System.Security.Cryptography.X509Certificates.X509Certificate2 In signCertChain
                    padding += "    "
                    System.Console.WriteLine("{0}Serial number: {1}", padding, cert.SerialNumber)
                    System.Console.WriteLine("{0}Issuer       : {1}", padding, cert.GetNameInfo(System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, True))
                    System.Console.WriteLine("{0}Subject      : {1}", padding, cert.GetNameInfo(System.Security.Cryptography.X509Certificates.X509NameType.SimpleName, False))
                Next


                ' verify digital signature
                VerifyDigitalSignature(signatureInfo, signature)
            End If
            System.Console.WriteLine()
        Next
    End Using
End Sub

''' <summary>
''' Verifies the digital signature.
''' </summary>
''' <param name="signature">The signature.</param>
''' <param name="signatureInfo">The signature information.</param>
''' <returns><b>true</b> if signature is valid; otherwise, <b>false</b>.</returns>
Public Shared Function VerifyDigitalSignature(signatureInfo As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfSignatureInformation, signature As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature) As Boolean
    System.Console.WriteLine("Verifying signature...")

    Dim signatureVerifyResult As Boolean = False
    Dim embeddedTimestampVerifyResult As Boolean = False
    Dim certificateVerifyResult As Boolean = False
    Dim embeddedTimestampCertificateVerifyResult As Boolean = False
    Dim signatureCoversWholeDocument As Boolean = False
    Dim certificateChain As System.Security.Cryptography.X509Certificates.X509Chain = Nothing
    Dim timestampCertificateChain As System.Security.Cryptography.X509Certificates.X509Chain = Nothing


    ' verify signature

    Try
        ' check that signature covers the whole document
        signatureCoversWholeDocument = signatureInfo.SignatureCoversWholeDocument()

        ' verify PKCS signature
        signatureVerifyResult = signature.VerifySignature()

        ' if signature has embedded timestamp
        If signature.HasEmbeddedTimeStamp Then
            ' verify embedded timestamp
            embeddedTimestampVerifyResult = signature.VerifyTimestamp()
        End If

        ' build and verify certificate chain
        certificateChain = New System.Security.Cryptography.X509Certificates.X509Chain()
        certificateVerifyResult = certificateChain.Build(signature.SigningCertificate)

        ' if signature has embedded timestamp
        If signature.HasEmbeddedTimeStamp Then
            ' build and verify timestamp certificate chain
            timestampCertificateChain = New System.Security.Cryptography.X509Certificates.X509Chain()
            embeddedTimestampCertificateVerifyResult = certificateChain.Build(signature.TimestampCertificate)

        End If
    Catch verificationException As System.Exception
        System.Console.WriteLine("Verification failed: {0}", verificationException.Message)
        Return False
    End Try

    Dim pageContentModified As Boolean = False
    Dim subsequentChangesMessage As String = ""
    ' if PKCS signature verification is passed AND signature does not cover the whole document
    If signatureVerifyResult AndAlso Not signatureCoversWholeDocument Then
        Try
            ' if signature has revision info
            If signatureInfo.SignedRevision IsNot Nothing Then
                ' check subsequent changes
                Using documentChanges As Vintasoft.Imaging.Pdf.PdfDocumentRevisionComparer = signatureInfo.GetDocumentChanges()
                    ' check subsequent changes in pages content
                    pageContentModified = documentChanges.HasModifiedPages

                    ' build subsequent changes message
                    If documentChanges.ChangedPageContents.Count > 0 Then
                        subsequentChangesMessage += String.Format("{0} page(s) modified; ", documentChanges.ChangedPageContents.Count)
                    End If
                    If documentChanges.AddedPages.Count > 0 Then
                        subsequentChangesMessage += String.Format("{0} page(s) added; ", documentChanges.AddedPages.Count)
                    End If
                    If documentChanges.RemovedPages.Count > 0 Then
                        subsequentChangesMessage += String.Format("{0} page(s) removed; ", documentChanges.RemovedPages.Count)
                    End If
                    If documentChanges.RemovedAnnotations.Count > 0 Then
                        subsequentChangesMessage += String.Format("annotations(s) on {0} page(s) removed; ", documentChanges.RemovedAnnotations.Count)
                    End If
                    If documentChanges.RemovedAnnotations.Count > 0 Then
                        subsequentChangesMessage += String.Format("removed annotation(s) on {0} page(s); ", documentChanges.RemovedAnnotations.Count)
                    End If
                    If documentChanges.AddedAnnotations.Count > 0 Then
                        subsequentChangesMessage += String.Format("added annotation(s) on {0} page(s); ", documentChanges.AddedAnnotations.Count)
                    End If
                    If documentChanges.ChangedAnnotations.Count > 0 Then
                        subsequentChangesMessage += String.Format("changed annotation(s) on {0} page(s); ", documentChanges.ChangedAnnotations.Count)
                    End If
                    If documentChanges.MiscellaneousChanges.Count > 0 Then
                        subsequentChangesMessage += String.Format("miscellaneous changes: {0}; ", documentChanges.MiscellaneousChanges.Count)
                    End If
                End Using
            End If
        Catch verificationException As System.Exception
            System.Console.WriteLine("Verification failed: {0}", verificationException.Message)
            Return False
        End Try
    End If

    ' print signature verification result

    ' if PKCS signature verification is failed OR
    ' signature does not cover the whole document AND page(s) content is modified
    If Not signatureVerifyResult OrElse (Not signatureCoversWholeDocument AndAlso pageContentModified) Then
        System.Console.WriteLine("Signature is INVALID.")
    ' if certificate verification is failed
    ElseIf Not certificateVerifyResult OrElse (signature.HasEmbeddedTimeStamp AndAlso (Not embeddedTimestampCertificateVerifyResult OrElse Not embeddedTimestampVerifyResult)) Then
        System.Console.WriteLine("Signature validity is UNKNOWN.")
    Else
        System.Console.WriteLine("Signature is VALID.")
    End If


    ' print signature verification details

    ' if signature verification is successful
    If signatureVerifyResult Then
        ' if signature covers the whole document
        If signatureCoversWholeDocument Then
            System.Console.WriteLine("    Signature verification: Document has not been modified since this signature was applied.")
        Else
            ' if signature does NOT cover the whole document
            If pageContentModified Then
                System.Console.WriteLine("    Signature verification: Document has been modified or corrupted since it was signed.")
                System.Console.WriteLine(String.Format("    Subsequent changes: {0}.", subsequentChangesMessage))
            ElseIf subsequentChangesMessage <> "" Then
                System.Console.WriteLine("    Signature verification: The revision of the document that was covered by this signature has not been altered; however, there have been subsequent changes to the document.")
                System.Console.WriteLine(String.Format("    Subsequent changes: {0}.", subsequentChangesMessage))
            Else
                System.Console.WriteLine("    Signature verification: Document has not been modified since this signature was applied.")
            End If
        End If
    Else
        ' if signature verification is NOT successful
        System.Console.WriteLine("    Signature verification: Document has been modified or corrupted since it was signed.")
    End If

    ' if signature has embedded timestamp
    If signature.HasEmbeddedTimeStamp Then
        If embeddedTimestampVerifyResult Then
            System.Console.WriteLine("    Timestamp verification: Timestamp is valid.")
        Else
            System.Console.WriteLine("    Timestamp verification: Timestamp is valid.")
        End If
    End If


    ' print certificate verification details

    ' if certificate chain is present
    If certificateChain IsNot Nothing Then
        ' if certificate verification is successful
        If certificateVerifyResult Then
            System.Console.WriteLine("    Certificate verification: Signer's certificate is valid.")
        Else
            ' if certificate verification is NOT successful
            ' print certificate verification status
            System.Console.WriteLine("    Certificate verification: Signer's certificate is invalid:")
            For Each status As System.Security.Cryptography.X509Certificates.X509ChainStatus In certificateChain.ChainStatus
                System.Console.Write(String.Format("        {0}: {1}", status.Status, status.StatusInformation))
            Next
        End If
    End If

    ' if timestamp certificate chain is present
    If timestampCertificateChain IsNot Nothing Then
        ' if timestamp certificate verification is successful
        If embeddedTimestampCertificateVerifyResult Then
            System.Console.WriteLine("    Timestamp certificate verification: Signer's certificate is valid.")
        Else
            ' if timestamp certificate verification is NOT successful
            ' print certificate verification status
            System.Console.WriteLine("    Timestamp certificate verification: Signer's certificate is invalid:")
            For Each status As System.Security.Cryptography.X509Certificates.X509ChainStatus In timestampCertificateChain.ChainStatus
                System.Console.Write(String.Format("        {0}: {1}", status.Status, status.StatusInformation))
            Next
        End If
    End If

    ' if signature is not verified
    If Not signatureVerifyResult Then
        Return False
    End If

    ' if signature does NOT cover the whole document and page content was modified
    If Not signatureCoversWholeDocument AndAlso pageContentModified Then
        Return False
    End If

    ' if signature certificate is NOT verified
    If Not certificateVerifyResult Then
        Return False
    End If

    If signature.HasEmbeddedTimeStamp Then
        ' if timestamp is NOT verified
        If Not embeddedTimestampVerifyResult Then
            Return False
        End If

        ' if timestamp certifiacet is NOT verified
        If Not embeddedTimestampCertificateVerifyResult Then
            Return False
        End If
    End If

    ' sigature is VALID
    Return True
End Function

/// <summary>
/// Removes all digital signatures from PDF document.
/// </summary>
/// <param name="pdfFilename">The filename of PDF document.</param>
public static void RemoveDigitalSignaturesFromPdfDocument(string pdfFilename)
{
    // open PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document =
        new Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename))
    {
        // if PDF document has PDF interactive form
        if (document.InteractiveForm != null)
        {
            // get reference to the interactive form of PDF document
            Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentInteractiveForm form =
                document.InteractiveForm;

            // get all signature fields of PDF document
            Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField[] signatureFields =
                form.GetSignatureFields();

            // for each signature fields
            foreach (Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormField field in signatureFields)
            {
                // remove signature field
                field.Remove();
            }

            // pack PDF document
            document.Pack();
        }
    }
}

''' <summary>
''' Removes all digital signatures from PDF document.
''' </summary>
''' <param name="pdfFilename">The filename of PDF document.</param>
Public Shared Sub RemoveDigitalSignaturesFromPdfDocument(pdfFilename As String)
    ' open PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename)
        ' if PDF document has PDF interactive form
        If document.InteractiveForm IsNot Nothing Then
            ' get reference to the interactive form of PDF document
            Dim form As Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfDocumentInteractiveForm = document.InteractiveForm

            ' get all signature fields of PDF document
            Dim signatureFields As Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormSignatureField() = form.GetSignatureFields()

            ' for each signature fields
            For Each field As Vintasoft.Imaging.Pdf.Tree.InteractiveForms.PdfInteractiveFormField In signatureFields
                ' remove signature field
                field.Remove()
            Next

            ' pack PDF document
            document.Pack()
        End If
    End Using
End Sub