Delphi ActiveX 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 ActiveX

var
success: Integer;
pdf: TChilkatPdf;
json: TChilkatJsonObject;
jsonOut: TChilkatJsonObject;
sigInfo: TChilkatJsonObject;
validated: Integer;

begin
success := 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 := TChilkatPdf.Create(Self);
success := pdf.LoadFile('qa_data/pdf/invoice_signed.pdf');
if (success = 0) then
  begin
    Memo1.Lines.Add(pdf.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('Signatures: ' + IntToStr(pdf.NumSignatures));

json := TChilkatJsonObject.Create(Self);
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 := TChilkatJsonObject.Create(Self);
success := pdf.TextReplace('check',json.ControlInterface,jsonOut.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(pdf.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('check: ok = ' + IntToStr(Ord(jsonOut.BoolOf('ok'))));

//  "apply" is refused while PreserveSignatures is true (the default).
success := pdf.TextReplace('apply',json.ControlInterface,jsonOut.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add('apply refused: ' + pdf.LastErrorText);
  end;

//  Allowing the signature to be broken:
pdf.PreserveSignatures := 0;
success := pdf.TextReplace('apply',json.ControlInterface,jsonOut.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(pdf.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('applied: ' + IntToStr(Ord(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 = 0) then
  begin
    Memo1.Lines.Add(pdf.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('Signatures after writing: ' + IntToStr(pdf.NumSignatures));
sigInfo := TChilkatJsonObject.Create(Self);
validated := pdf.VerifySignature(0,sigInfo.ControlInterface);
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