Lazarus Pascal Requires Chilkat v11.7.0+

Optimizing a Signed PDF (PreserveSignatures)

See more PDF Optimization Examples

Demonstrates what happens when a signed PDF is optimized. Optimizing rewrites the document, and a rewrite breaks every existing digital signature, so with PreserveSignatures true (the default) Optimize refuses and LastErrorText says why. Setting PreserveSignatures to false allows it, and the signature that was in the file no longer verifies afterwards. "audit" is always allowed, because it changes nothing. Lazarus Pascal

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Pdf,
  Chilkat.JsonObject;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  pdf: TPdf;
  json: TJsonObject;
  jsonOut: TJsonObject;
  pdf2: TPdf;
  sigInfo: TJsonObject;
  verified: 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 := TPdf.Create;
  success := pdf.LoadFile('qa_data/pdf/invoice_signed.pdf');
  if (success = False) then
    begin
      WriteLn(pdf.LastErrorText);
      Exit;
    end;

  WriteLn('signatures: ' + pdf.NumSignatures);

  json := TJsonObject.Create;
  jsonOut := TJsonObject.Create;

  //  An audit changes nothing, so it is allowed on a signed PDF.
  success := pdf.Optimize('audit',json,jsonOut);
  if (success = False) then
    begin
      WriteLn(pdf.LastErrorText);
      Exit;
    end;
  WriteLn('audit ok, estimated savings: ' + jsonOut.IntOf('estimatedSavings.total'));

  //  Optimizing is refused while PreserveSignatures is true.
  success := pdf.Optimize('optimize',json,jsonOut);
  if (success = False) then
    begin
      WriteLn('Refused while PreserveSignatures is true.');
    end;

  //  Allow the rewrite.  Do this only when the signatures no longer matter -- an invoice being
  //  archived, say, where the signed original is kept elsewhere.
  pdf.PreserveSignatures := False;
  success := pdf.Optimize('optimize',json,jsonOut);
  if (success = False) then
    begin
      WriteLn(pdf.LastErrorText);
      Exit;
    end;
  success := pdf.WriteFile('qa_output/invoice_optimized.pdf');
  if (success = False) then
    begin
      WriteLn(pdf.LastErrorText);
      Exit;
    end;
  WriteLn('optimized, bytesSaved: ' + jsonOut.IntOf('bytesSaved'));

  //  The signature is still in the file, but it no longer verifies: the bytes it covered have changed.
  pdf2 := TPdf.Create;
  success := pdf2.LoadFile('qa_output/invoice_optimized.pdf');
  if (success = False) then
    begin
      WriteLn(pdf2.LastErrorText);
      Exit;
    end;
  WriteLn('signatures after: ' + pdf2.NumSignatures);

  sigInfo := TJsonObject.Create;
  verified := pdf2.VerifySignature(0,sigInfo);
  WriteLn('verifies after optimizing: ' + verified);


  pdf.Free;
  json.Free;
  jsonOut.Free;
  pdf2.Free;
  sigInfo.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.