Go 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. Go

    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.NewPdf()
    success = pdf.LoadFile("qa_data/pdf/invoice_signed.pdf")
    if success == false {
        fmt.Println(pdf.LastErrorText())
        pdf.DisposePdf()
        return
    }

    fmt.Println("Signatures: ", pdf.NumSignatures())

    json := chilkat.NewJsonObject()
    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.NewJsonObject()
    success = pdf.TextReplace("check",json,jsonOut)
    if success == false {
        fmt.Println(pdf.LastErrorText())
        pdf.DisposePdf()
        json.DisposeJsonObject()
        jsonOut.DisposeJsonObject()
        return
    }

    fmt.Println("check: ok = ", *jsonOut.BoolOf("ok"))

    //  "apply" is refused while PreserveSignatures is true (the default).
    success = pdf.TextReplace("apply",json,jsonOut)
    if success == false {
        fmt.Println("apply refused: ", pdf.LastErrorText())
    }

    //  Allowing the signature to be broken:
    pdf.SetPreserveSignatures(false)
    success = pdf.TextReplace("apply",json,jsonOut)
    if success == false {
        fmt.Println(pdf.LastErrorText())
        pdf.DisposePdf()
        json.DisposeJsonObject()
        jsonOut.DisposeJsonObject()
        return
    }

    fmt.Println("applied: ", *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 {
        fmt.Println(pdf.LastErrorText())
        pdf.DisposePdf()
        json.DisposeJsonObject()
        jsonOut.DisposeJsonObject()
        return
    }

    fmt.Println("Signatures after writing: ", pdf.NumSignatures())
    sigInfo := chilkat.NewJsonObject()
    validated := pdf.VerifySignature(0,sigInfo)
    fmt.Println("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

    pdf.DisposePdf()
    json.DisposeJsonObject()
    jsonOut.DisposeJsonObject()
    sigInfo.DisposeJsonObject()