title: mPDF library: force download file
body: <p>Hi I treid to generate a simple pdf file using mPDF library but, when I force the download of the file I obtain an Error code 500.</p>
  
  <p>this is my code:</p>
  
  <pre><code>$mpdf=new mPDF('c','A4','','',20,20,47,47,10,10); 
  $mpdf-&gt;SetHTMLHeader($header);
  $mpdf-&gt;SetHTMLFooter($footer);
  $mpdf-&gt;WriteHTML($html);
  $mpdf-&gt;Output("my_filename.pdf","D");
  </code></pre>