PDF as Watermark

procedure TForm1.TestnonvisualPDFworkbench1Click(Sender: TObject);
var workbench : Pointer;
    s : String;
    function CommandGetString(
              id : Integer;
              strparam : String = '';
              intparam : Integer = 0 ) : String;
    var
      i: Integer;
    begin
      i := wpview_pdfWorkbenchCommand(workbench,id, intparam, PWideChar(strparam), nil);
      if i > 0 then
      begin
        SetLength(Result, i);
        wpview_pdfWorkbenchCommand(workbench, COMPDF_GetTextBufW, 0, nil, (@Result[1]) );
      end
      else
        Result := '';
    end;
begin
  if OpenDialog1.Execute then
  begin
   if not assigned(wpview_pdfWorkbenchCreate) then
     raise Exception.Create('wpview_pdfWorkbenchCreate is not available');
   workbench := wpview_pdfWorkbenchCreate(PWideChar(LicName), PWideChar(LicKey), LicCode );
   if not assigned(workbench) then
     raise Exception.Create('wpview_pdfWorkbenchCreate failed');
   try
     s := OpenDialog1.FileName;
     if wpview_pdfWorkbenchLoad( workbench, PWideChar(s), 0 , 0 )<0 then
         raise Exception.Create('wpview_pdfWorkbenchLoad failed');
     ShowMessage(
       Format('This PDF File has %d pages. DLL-Version = %s', [
        wpview_pdfWorkbenchCommand( workbench, COMPDF_GetPageCount, 0, nil, nil ),
        CommandGetString(COMPDF_GET_DLLVERSION)
         ] )
        );
   finally
     wpview_pdfWorkbenchFree( workbench );
   end;
  end;
end;