CkPython 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. CkPython

import sys
import chilkat

success = 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

pdf = chilkat.CkPdf()
success = pdf.LoadFile("qa_data/pdf/invoice_signed.pdf")
if (success == False):
    print(pdf.lastErrorText())
    sys.exit()

print("Signatures: " + str(pdf.get_NumSignatures()))

json = chilkat.CkJsonObject()
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.
jsonOut = chilkat.CkJsonObject()
success = pdf.TextReplace("check",json,jsonOut)
if (success == False):
    print(pdf.lastErrorText())
    sys.exit()

print("check: ok = " + str(jsonOut.BoolOf("ok")))

#  "apply" is refused while PreserveSignatures is true (the default).
success = pdf.TextReplace("apply",json,jsonOut)
if (success == False):
    print("apply refused: " + pdf.lastErrorText())

#  Allowing the signature to be broken:
pdf.put_PreserveSignatures(False)
success = pdf.TextReplace("apply",json,jsonOut)
if (success == False):
    print(pdf.lastErrorText())
    sys.exit()

print("applied: " + str(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):
    print(pdf.lastErrorText())
    sys.exit()

print("Signatures after writing: " + str(pdf.get_NumSignatures()))
sigInfo = chilkat.CkJsonObject()
validated = pdf.VerifySignature(0,sigInfo)
print("Signature 0 verifies: " + str(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