Swift 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. Swift

func chilkatTest() {
    var success: Bool = 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

    let pdf = CkoPdf()!
    success = pdf.loadFile(filePath: "qa_data/pdf/invoice_signed.pdf")
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    print("Signatures: \(pdf.numSignatures.intValue)")

    let json = CkoJsonObject()!
    json.updateString(jsonPath: "labels[0].label", value: "Invoice Number:")
    json.updateString(jsonPath: "labels[0].value", value: "INV-2026-0500")

    //  "check" reads only, so it works on a signed PDF.
    let jsonOut = CkoJsonObject()!
    success = pdf.textReplace(op: "check", jsonIn: json, jsonOut: jsonOut)
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    print("check: ok = \(jsonOut.bool(of: "ok"))")

    //  "apply" is refused while PreserveSignatures is true (the default).
    success = pdf.textReplace(op: "apply", jsonIn: json, jsonOut: jsonOut)
    if success == false {
        print("apply refused: \(pdf.lastErrorText!)")
    }

    //  Allowing the signature to be broken:
    pdf.preserveSignatures = false
    success = pdf.textReplace(op: "apply", jsonIn: json, jsonOut: jsonOut)
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    print("applied: \(jsonOut.bool(of: "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(path: "qa_output/invoice_reissued_broken_signature.pdf")
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    print("Signatures after writing: \(pdf.numSignatures.intValue)")
    let sigInfo = CkoJsonObject()!
    var validated: Bool = pdf.verifySignature(index: 0, sigInfo: sigInfo)
    print("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

}