public static function respondPdf($responseID, $responseData = array())
 {
     if (!empty($_REQUEST['downloadToken'])) {
         setcookie('downloadToken', $_REQUEST['downloadToken'], time() + 300, '/');
     }
     $tmpPath = tempnam('/tmp', 'e_pdf_');
     file_put_contents($tmpPath . '.html', Emergence\Dwoo\Engine::getSource("{$responseID}.pdf", $responseData));
     header('Content-Type: application/pdf');
     header('Content-Disposition: attachment; filename="' . str_replace('"', '', $responseID) . '.pdf"');
     exec(static::$wkhtmltopdfPath . " \"{$tmpPath}.html\" \"{$tmpPath}.pdf\"");
     if (!file_exists("{$tmpPath}.pdf")) {
         header('HTTP/1.0 501 Not Implemented');
         die('Unable to generate PDF, check that this system has wkhtmltopdf installed');
     }
     readfile($tmpPath . '.pdf');
     exit;
 }