Python 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. Chilkat2-Python

import sys
import chilkat2

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 = chilkat2.Pdf()
success = pdf.LoadFile("qa_data/pdf/invoice_signed.pdf")
if (success == False):
    print(pdf.LastErrorText)
    sys.exit()

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

json = chilkat2.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.
jsonOut = chilkat2.JsonObject()
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.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.NumSignatures))
sigInfo = chilkat2.JsonObject()
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