/**
  * Generate the PDF filename according to md5 and options
  * 
  * @param   string  $md5      The md5 of the URL or content
  * @param   array   $options  The options table
  * @return  string            The absolute PDF file (with path)
  * @access  private
  * @static
  * @since   1.0.0
  */
 private static function getPdfTmpFilename($md5, $options = array())
 {
     $folder = ApiPrint::getPdfTmpFolder();
     $filename = sha1($md5 . serialize($options));
     return $folder . '/' . $filename . '.pdf';
 }