C 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. C

#include <C_CkPdf.h>
#include <C_CkJsonObject.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkPdf pdf;
    HCkJsonObject json;
    HCkJsonObject jsonOut;
    HCkJsonObject sigInfo;
    BOOL validated;

    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 = CkPdf_Create();
    success = CkPdf_LoadFile(pdf,"qa_data/pdf/invoice_signed.pdf");
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        return;
    }

    printf("Signatures: %d\n",CkPdf_getNumSignatures(pdf));

    json = CkJsonObject_Create();
    CkJsonObject_UpdateString(json,"labels[0].label","Invoice Number:");
    CkJsonObject_UpdateString(json,"labels[0].value","INV-2026-0500");

    //  "check" reads only, so it works on a signed PDF.
    jsonOut = CkJsonObject_Create();
    success = CkPdf_TextReplace(pdf,"check",json,jsonOut);
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkJsonObject_Dispose(jsonOut);
        return;
    }

    printf("check: ok = %d\n",CkJsonObject_BoolOf(jsonOut,"ok"));

    //  "apply" is refused while PreserveSignatures is true (the default).
    success = CkPdf_TextReplace(pdf,"apply",json,jsonOut);
    if (success == FALSE) {
        printf("apply refused: %s\n",CkPdf_lastErrorText(pdf));
    }

    //  Allowing the signature to be broken:
    CkPdf_putPreserveSignatures(pdf,FALSE);
    success = CkPdf_TextReplace(pdf,"apply",json,jsonOut);
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkJsonObject_Dispose(jsonOut);
        return;
    }

    printf("applied: %d\n",CkJsonObject_BoolOf(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_WriteFile(pdf,"qa_output/invoice_reissued_broken_signature.pdf");
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkJsonObject_Dispose(jsonOut);
        return;
    }

    printf("Signatures after writing: %d\n",CkPdf_getNumSignatures(pdf));
    sigInfo = CkJsonObject_Create();
    validated = CkPdf_VerifySignature(pdf,0,sigInfo);
    printf("Signature 0 verifies: %d\n",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_Dispose(pdf);
    CkJsonObject_Dispose(json);
    CkJsonObject_Dispose(jsonOut);
    CkJsonObject_Dispose(sigInfo);

    }