PureBasic 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. PureBasic

IncludeFile "CkPdf.pb"
IncludeFile "CkJsonObject.pb"

Procedure ChilkatExample()

    success.i = 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

    pdf.i = CkPdf::ckCreate()
    If pdf.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPdf::ckLoadFile(pdf,"qa_data/pdf/invoice_signed.pdf")
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        ProcedureReturn
    EndIf

    Debug "Signatures: " + Str(CkPdf::ckNumSignatures(pdf))

    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckUpdateString(json,"labels[0].label","Invoice Number:")
    CkJsonObject::ckUpdateString(json,"labels[0].value","INV-2026-0500")

    ;  "check" reads only, so it works on a signed PDF.
    jsonOut.i = CkJsonObject::ckCreate()
    If jsonOut.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPdf::ckTextReplace(pdf,"check",json,jsonOut)
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    Debug "check: ok = " + Str(CkJsonObject::ckBoolOf(jsonOut,"ok"))

    ;  "apply" is refused while PreserveSignatures is true (the default).
    success = CkPdf::ckTextReplace(pdf,"apply",json,jsonOut)
    If success = 0
        Debug "apply refused: " + CkPdf::ckLastErrorText(pdf)
    EndIf

    ;  Allowing the signature to be broken:
    CkPdf::setCkPreserveSignatures(pdf, 0)
    success = CkPdf::ckTextReplace(pdf,"apply",json,jsonOut)
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    Debug "applied: " + Str(CkJsonObject::ckBoolOf(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.
    success = CkPdf::ckWriteFile(pdf,"qa_output/invoice_reissued_broken_signature.pdf")
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    Debug "Signatures after writing: " + Str(CkPdf::ckNumSignatures(pdf))
    sigInfo.i = CkJsonObject::ckCreate()
    If sigInfo.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    validated.i = CkPdf::ckVerifySignature(pdf,0,sigInfo)
    Debug "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


    CkPdf::ckDispose(pdf)
    CkJsonObject::ckDispose(json)
    CkJsonObject::ckDispose(jsonOut)
    CkJsonObject::ckDispose(sigInfo)


    ProcedureReturn
EndProcedure