title: Double signature on pdf already signed
body: <p>I have this script which already sign a PDF</p>
  
  <pre><code>&lt;?php
  require("../config/include.php");
  require_once(DIR_LIBRERIAS."TCPDF/tcpdf.php");
  require_once(DIR_LIBRERIAS.'FPDI/fpdi.php');
  //$pdf = new TCPDF(PDF_PAGE_ORIENTATION);
  
  error_reporting(0);
  // set certificate file
  $certificate = 'file://'.DIR_ROOT.'cert/testcertif.crt';
  $pdf = new FPDI();
  $filename = "zz_test_firmado.pdf";
  $info = array('Name' =&gt; 'testcertif', 'Location' =&gt; 'Oficina', 'Reason' =&gt; 'test firma', 'ContactInfo' =&gt; 'test.com.ar');
  
  $pdf-&gt;setSignature($certificate, $certificate, 'test key pass', '', 2, $info);
  
  $pdf-&gt;setPrintHeader(false);
  $pdf-&gt;setPrintFooter(false);
  $pages_count= $pdf-&gt;setSourceFile($filename);
  $page = "P";
  
  for($i = 1; $i &lt;= $pages_count; $i++)
  {
      $tplIdx = $pdf-&gt;importPage($i);
      $size = $pdf-&gt;getTemplateSize($tplIdx);
      if ($size['w'] &gt; $size['h']) {
          $pdf-&gt;AddPage('L', array($size['w'], $size['h']));
          $arrayUltimo = array($size['w'], $size['h']);
          $page = "L";
      } else {
          $pdf-&gt;AddPage('P', array($size['w'], $size['h']));
          $arrayUltimo = array($size['w'], $size['h']);
      }
  
      $pdf-&gt;useTemplate($tplIdx, 0, 0, 0, 0, true);
  
  }
  
  $pdf-&gt;output('testfirmass222.pdf', 'I');
  
  ?&gt;
  </code></pre>
  
  <p>However, when the pdf that i'm importing already has a signature, the signature is replaced by the new one put on the script, is there a way to keep both?</p>