/**
  * @see EPSInterface::createPDF()
  */
 public function createPDF($sessionId, $params)
 {
     try {
         $createPDFStdObject = new stdClass();
         $createPDFStdObject->sessionId = $sessionId;
         $createPDFStdObject->params = $params->toStdClass();
         $response = parent::createPDF($createPDFStdObject);
         if (isset($response->return)) {
             $resultPDF = $response->return;
         } else {
             $resultPDF = null;
         }
         return $resultPDF;
     } catch (SoapFault $sf) {
         throw new ServerException($sf);
     }
 }