PDFsharp & MigraDoc Foundation

Imports PdfSharp.Pdf
Imports PdfSharp.Pdf.Advanced
Imports PdfSharp.Pdf.Content
Imports PdfSharp.Pdf.Content.Objects
Imports PdfSharp.Pdf.IO

    Private Sub ParseAndModifyContent(input As String, output As String)

        Using pdfdoc As PdfDocument = PdfReader.Open(input, PdfDocumentOpenMode.Modify)
            Dim page As PdfPage
            Dim pagecount As Integer = pdfdoc.PageCount
            'loop all pages
            For ipage As Integer = 0 To pagecount - 1
                page = pdfdoc.Pages(ipage)
                Dim contents As CSequence = ContentReader.ReadContent(page)
                Call ProcessContentObjects(contents)
                page.Contents.ReplaceContent(contents)

                Dim pdfres As PdfResources = page.Resources
                Call ProcessResources(pdfres)

            Next
            'save modified file
            pdfdoc.Save(output)
        End Using

    End Sub

Private Sub ProcessContentObjects(contents As Objects.CSequence)
        Dim cOp As COperator
        'loop all content objects
        For i As Integer = 0 To contents.Count - 1
            If contents(i).GetType Is GetType(COperator) Then
                cOp = contents(i)
                Debug.WriteLine(cOp.OpCode.Name & " - " & cOp.OpCode.Postscript & " - " & cOp.OpCode.Description)
                'do anything needed with this Operator and its Operands
                'this part works fine
            End If
        Next
    End Sub

    Private Sub ProcessResources(res As PdfDictionary)
        'check if XObjects exist
        If res IsNot Nothing AndAlso res.Elements.ContainsKey(PdfResources.Keys.XObject) Then
            Dim xObj As PdfDictionary = res.Elements.GetDictionary(PdfResources.Keys.XObject)
            If xObj IsNot Nothing Then
                Dim items As ICollection(Of PdfItem) = xObj.Elements.Values
                For Each item As PdfItem In items
                    If item.GetType Is GetType(PdfReference) Then
                        Dim ref As PdfReference = DirectCast(item, PdfReference)
                        Debug.WriteLine("ObjectNumber = " & ref.ObjectNumber) 'avoid processing endless recursions using this number if needed
                        Dim xObj2 As PdfDictionary = ref.Value
                        'check if Subtype is /Form
                        If xObj2.Elements.GetString("/Subtype") = "/Form" Then
                            'get content bytes of stream
                            Dim stream As PdfDictionary.PdfStream = xObj2.Stream
                            'check if a content stream exists
                            If stream IsNot Nothing Then
                                'get unfiltered/uncompressed bytes
                                Dim contentbytes() As Byte = stream.UnfilteredValue
                                Dim encoder As Internal.RawEncoding = New PdfSharp.Pdf.Internal.RawEncoding()
                                'get stream content as string to check visually
                                Dim content_string As String = encoder.GetString(contentbytes)
                                Debug.WriteLine(content_string)
                                'get content objects
                                Dim contents As CSequence = ContentReader.ReadContent(contentbytes)
                                'process content objects same as page contents
                                Call ProcessContentObjects(contents)
                                '--------PROBLEM STARTS HERE
                                '1-How do I turn the modified content object back into a byte array
                                '2-How do I attach that byte array back to the Stream object
                                '3-How do I persist the modified Stream in the Resource dictionary, so pdfDoc.Save will save changes ?
                                'testing with unmodified content, just writing same bytes back
                                Dim modifiedcontentbytes() As Byte = contentbytes.Clone
                                'write modified content back to stream and compress
                                '-------THIS PART FAILS-------Output PDF has no Stream, but no error in code
                                xObj2.Stream = Nothing
                                xObj2.Stream = xObj2.CreateStream(modifiedcontentbytes)
                                xObj2.Stream.Zip()

                            End If
                            'get nested resources if they exist
                            Dim res2 As PdfDictionary = xObj2.Elements.GetDictionary("/Resources")
                            'recursive call
                            If res2 IsNot Nothing Then Call ProcessResources(res2)

                        ElseIf xObj2.Elements.GetString("/Subtype") = "/Image" Then
                            'process anything for /Image
                        Else
                            'process anything for other Subtypes
                            Debug.WriteLine(xObj2.Elements.GetString("/Subtype"))
                        End If
                    End If
                Next
            End If
        End If
    End Sub

xObj2.Stream = xObj2.CreateStream(modifiedcontentbytes)

xObj2.Stream.Zip()

'Remove existing filter
xObj2.Elements.Remove("/Filter")
' Set new value for stream (has the same effect as creating a new stream)
xObj2.Stream.Value = modifiedcontentbytes
' Zip it, this creates a new /Filter -entry in the parent-dictionary
xObj2.Stream.Zip()

Dim contents As CSequence = ContentReader.ReadContent(contentbytes) 'works
Call ProcessContentObjects(contents) 'works
'I cannot find a method to convert modified object of type CSequence back to a byte array.
Dim modifiedcontentbytes() As Byte = ContentWriter.WriteContentFromObjects(contents)   'looking for something like this

Dim contents As CSequence = ContentReader.ReadContent(page)
Call ProcessContentObjects(contents)
page.Contents.ReplaceContent(contents)

Dim pdfres As PdfResources = page.Resources  'works
Call ProcessResources(pdfres)  'works
page.Resources.ReplaceResources(pdfres)  'there is no such method

Dim modifiedcontentbytes() As Byte = contents.ToContent