protected function sendHeaders($tmpFile)
    {
        header('Pragma: public');
        header('Expires: 0');
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Content-Type: application/pdf');
        header('Content-Transfer-Encoding: binary');
        header('Content-Length: ' . filesize($tmpFile));
    }