VB.NET Requires Chilkat v11.7.0+

Replace Text in a Signed PDF (PreserveSignatures)

See more PDF Text Replacement Examples

Applying a text replacement rewrites the page content, which invalidates any digital signature on the PDF. While the PreserveSignatures property is true (the default), "apply" is refused on a signed PDF; "check" only reads and is always allowed. Setting PreserveSignatures to false allows the replacement; the signature field stays in the written PDF but no longer verifies, so the document should be signed again afterwards if a signature is wanted. 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
json.UpdateString("labels[0].label","Invoice Number:")
json.UpdateString("labels[0].value","INV-2026-0500")

'  "check" reads only, so it works on a signed PDF.
Dim jsonOut As New Chilkat.JsonObject
success = pdf.TextReplace("check",json,jsonOut)
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("check: ok = " & jsonOut.BoolOf("ok"))

'  "apply" is refused while PreserveSignatures is true (the default).
success = pdf.TextReplace("apply",json,jsonOut)
If (success = False) Then
    Debug.WriteLine("apply refused: " & pdf.LastErrorText)
End If


'  Allowing the signature to be broken:
pdf.PreserveSignatures = False
success = pdf.TextReplace("apply",json,jsonOut)
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("applied: " & jsonOut.BoolOf("applied"))

'  The written PDF is a full rewrite with the replacement.  The signature field is still in the document,
'  but the bytes it signed are gone, so it no longer verifies.
success = pdf.WriteFile("qa_output/invoice_reissued_broken_signature.pdf")
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("Signatures after writing: " & pdf.NumSignatures)
Dim sigInfo As New Chilkat.JsonObject
Dim validated As Boolean = pdf.VerifySignature(0,sigInfo)
Debug.WriteLine("Signature 0 verifies: " & validated)

'  Sample output:

'  Signatures: 1
'  check: ok = true
'  apply refused: ChilkatLog:
'    TextReplace:
'      DllDate: Nov  7 2026
'      ChilkatVersion: 11.7.0
'      UnlockPrefix: CHLKAT
'      UnlockStatus: 2
'      Architecture: Little Endian; 64-bit
'      Language: Visual C++ 11.0 / x64
'      VerboseLogging: 0
'      replaceTextOp:
'        op: apply
'        The PDF is signed: replacing text rewrites the content and invalidates the signatures (set PreserveSignatures = false to allow it).
'      --replaceTextOp
'      Failed.
'    --TextReplace
'  --ChilkatLog
'  
'  applied: true
'  Signatures after writing: 1
'  Signature 0 verifies: false