/**
  * Get Invoice pdf by Invoice number
  *
  * @param integer $no
  * @param bool|false $download
  * @return bool
  */
 public function pdf($no, $download = false)
 {
     $handle = $this->getHandle($no);
     $pdf = $this->client->Invoice_GetPdf(['invoiceHandle' => $handle])->Invoice_GetPdfResult;
     if ($download) {
         header('Content-type: application/pdf');
         header('Content-Disposition: attachment; filename="' . $no . '.pdf"');
         echo $pdf;
         return true;
     }
     return $pdf;
 }