/// <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.ContactInfo));
                // 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.ContactInfo))
                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