Delphi DLL 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. Delphi DLL

var
success: Boolean;
pdf: HCkPdf;
json: HCkJsonObject;
jsonOut: HCkJsonObject;
sigInfo: HCkJsonObject;
validated: Boolean;

begin
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) then
  begin
    Memo1.Lines.Add(CkPdf__lastErrorText(pdf));
    Exit;
  end;
Memo1.Lines.Add('Signatures: ' + IntToStr(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) then
  begin
    Memo1.Lines.Add(CkPdf__lastErrorText(pdf));
    Exit;
  end;
Memo1.Lines.Add('check: ok = ' + IntToStr(Ord(CkJsonObject_BoolOf(jsonOut,'ok'))));

//  "apply" is refused while PreserveSignatures is true (the default).
success := CkPdf_TextReplace(pdf,'apply',json,jsonOut);
if (success = False) then
  begin
    Memo1.Lines.Add('apply refused: ' + CkPdf__lastErrorText(pdf));
  end;

//  Allowing the signature to be broken:
CkPdf_putPreserveSignatures(pdf,False);
success := CkPdf_TextReplace(pdf,'apply',json,jsonOut);
if (success = False) then
  begin
    Memo1.Lines.Add(CkPdf__lastErrorText(pdf));
    Exit;
  end;
Memo1.Lines.Add('applied: ' + IntToStr(Ord(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) then
  begin
    Memo1.Lines.Add(CkPdf__lastErrorText(pdf));
    Exit;
  end;
Memo1.Lines.Add('Signatures after writing: ' + IntToStr(CkPdf_getNumSignatures(pdf)));
sigInfo := CkJsonObject_Create();
validated := CkPdf_VerifySignature(pdf,0,sigInfo);
Memo1.Lines.Add('Signature 0 verifies: ' + IntToStr(Ord(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);