' The project, which uses this code, must have references to the following assemblies:
' - Vintasoft.Imaging
' - Vintasoft.Imaging.Pdf

''' <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)
        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, 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="sigNumber">The number of signature field.</param>
Private Shared Sub AddSignature(document As Vintasoft.Imaging.Pdf.PdfDocument, certificate As System.Security.Cryptography.X509Certificates.X509Certificate2, 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

        ' 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 PKCS#7 signature
        Dim signature As Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature = Vintasoft.Imaging.Pdf.Tree.DigitalSignatures.PdfPkcsSignature.CreatePkcs7Signature(certificate)

        ' 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

              

' The project, which uses this code, must have references to the following assemblies:
' - Vintasoft.Imaging.Pdf

''' <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 certificateVerifyResult As Boolean = False
        Dim signatureCoversWholeDocument As Boolean = False
        Dim chain 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.Verify()

                ' build and verify certificate chain
                Dim certificate As System.Security.Cryptography.X509Certificates.X509Certificate2 = signature.SigningCertificate
                chain = New System.Security.Cryptography.X509Certificates.X509Chain()
                certificateVerifyResult = chain.Build(certificate)
        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 modified
        If Not signatureVerifyResult OrElse (Not signatureCoversWholeDocument AndAlso pageContentModified) Then
                System.Console.WriteLine("Signature is INVALID.")
        ' if certificate verification is failed
        ElseIf Not certificateVerifyResult 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


        ' print certeficate verification details

        ' if certificate chain is present
        If chain 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 chain.ChainStatus
                                System.Console.Write(String.Format("        {0}: {1}", status.Status, status.StatusInformation))
                        Next
                End If
        End If

        Return signatureVerifyResult AndAlso (signatureCoversWholeDocument OrElse Not pageContentModified) AndAlso certificateVerifyResult
End Function
              

' The project, which uses this code, must have references to the following assemblies:
' - Vintasoft.Imaging.Pdf

''' <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