Xbase++ 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. Xbase++

LOCAL nSuccess
LOCAL oPdf
LOCAL oJson
LOCAL oJsonOut
LOCAL oSigInfo
LOCAL nValidated

nSuccess := 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

oPdf := CreateObject("Chilkat.Pdf")
nSuccess := oPdf:LoadFile("qa_data/pdf/invoice_signed.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    RETURN
ENDIF

? "Signatures: " + Str(oPdf:NumSignatures)

oJson := CreateObject("Chilkat.JsonObject")
oJson:UpdateString("labels[0].label", "Invoice Number:")
oJson:UpdateString("labels[0].value", "INV-2026-0500")

//  "check" reads only, so it works on a signed PDF.
oJsonOut := CreateObject("Chilkat.JsonObject")
nSuccess := oPdf:TextReplace("check", oJson, oJsonOut)
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oJsonOut:destroy()
    RETURN
ENDIF

? "check: ok = " + Str(oJsonOut:BoolOf("ok"))

//  "apply" is refused while PreserveSignatures is true (the default).
nSuccess := oPdf:TextReplace("apply", oJson, oJsonOut)
IF (nSuccess == 0)
    ? "apply refused: " + oPdf:LastErrorText
ENDIF

//  Allowing the signature to be broken:
oPdf:PreserveSignatures := 0
nSuccess := oPdf:TextReplace("apply", oJson, oJsonOut)
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oJsonOut:destroy()
    RETURN
ENDIF

? "applied: " + Str(oJsonOut: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.
nSuccess := oPdf:WriteFile("qa_output/invoice_reissued_broken_signature.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oJsonOut:destroy()
    RETURN
ENDIF

? "Signatures after writing: " + Str(oPdf:NumSignatures)
oSigInfo := CreateObject("Chilkat.JsonObject")
nValidated := oPdf:VerifySignature(0, oSigInfo)
? "Signature 0 verifies: " + Str(nValidated)

//  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

oPdf:destroy()
oJson:destroy()
oJsonOut:destroy()
oSigInfo:destroy()