Tcl 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. Tcl

load ./chilkat.dll

set success 0

#  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

set pdf [new_CkPdf]

set success [CkPdf_LoadFile $pdf "qa_data/pdf/invoice_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    exit
}

puts "Signatures: [CkPdf_get_NumSignatures $pdf]"

set json [new_CkJsonObject]

CkJsonObject_UpdateString $json "labels[0].label" "Invoice Number:"
CkJsonObject_UpdateString $json "labels[0].value" "INV-2026-0500"

#  "check" reads only, so it works on a signed PDF.
set jsonOut [new_CkJsonObject]

set success [CkPdf_TextReplace $pdf "check" $json $jsonOut]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

puts "check: ok = [CkJsonObject_BoolOf $jsonOut ok]"

#  "apply" is refused while PreserveSignatures is true (the default).
set success [CkPdf_TextReplace $pdf "apply" $json $jsonOut]
if {$success == 0} then {
    puts "apply refused: [CkPdf_lastErrorText $pdf]"
}

#  Allowing the signature to be broken:
CkPdf_put_PreserveSignatures $pdf 0
set success [CkPdf_TextReplace $pdf "apply" $json $jsonOut]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

puts "applied: [CkJsonObject_BoolOf $jsonOut 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.
set success [CkPdf_WriteFile $pdf "qa_output/invoice_reissued_broken_signature.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

puts "Signatures after writing: [CkPdf_get_NumSignatures $pdf]"
set sigInfo [new_CkJsonObject]

set validated [CkPdf_VerifySignature $pdf 0 $sigInfo]
puts "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

delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkJsonObject $jsonOut
delete_CkJsonObject $sigInfo