VB.NET Requires Chilkat v11.7.0+

Optimizing a Signed PDF (PreserveSignatures)

See more PDF Optimization Examples

Demonstrates what happens when a signed PDF is optimized. Optimizing rewrites the document, and a rewrite breaks every existing digital signature, so with PreserveSignatures true (the default) Optimize refuses and LastErrorText says why. Setting PreserveSignatures to false allows it, and the signature that was in the file no longer verifies afterwards. "audit" is always allowed, because it changes nothing. VB.NET

Dim success As Boolean = False

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

'  The PDF used in this example is available at invoice_signed.pdf

Dim pdf As New Chilkat.Pdf
success = pdf.LoadFile("qa_data/pdf/invoice_signed.pdf")
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("signatures: " & pdf.NumSignatures)

Dim json As New Chilkat.JsonObject
Dim jsonOut As New Chilkat.JsonObject

'  An audit changes nothing, so it is allowed on a signed PDF.
success = pdf.Optimize("audit",json,jsonOut)
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("audit ok, estimated savings: " & jsonOut.IntOf("estimatedSavings.total"))

'  Optimizing is refused while PreserveSignatures is true.
success = pdf.Optimize("optimize",json,jsonOut)
If (success = False) Then
    Debug.WriteLine("Refused while PreserveSignatures is true.")
End If


'  Allow the rewrite.  Do this only when the signatures no longer matter -- an invoice being
'  archived, say, where the signed original is kept elsewhere.
pdf.PreserveSignatures = False
success = pdf.Optimize("optimize",json,jsonOut)
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

success = pdf.WriteFile("qa_output/invoice_optimized.pdf")
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("optimized, bytesSaved: " & jsonOut.IntOf("bytesSaved"))

'  The signature is still in the file, but it no longer verifies: the bytes it covered have changed.
Dim pdf2 As New Chilkat.Pdf
success = pdf2.LoadFile("qa_output/invoice_optimized.pdf")
If (success = False) Then
    Debug.WriteLine(pdf2.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("signatures after: " & pdf2.NumSignatures)

Dim sigInfo As New Chilkat.JsonObject
Dim verified As Boolean = pdf2.VerifySignature(0,sigInfo)
Debug.WriteLine("verifies after optimizing: " & verified)