original_string: public function getInvoicePdf($letterId = null, $invoiceNo = null)
      {
          $params = array();
          if ($letterId)
              $params['letter_id'] = $letterId;
          if ($invoiceNo)
              $params['invoice_no'] = $invoiceNo;
  
          $response = $this->api->get(
              $this->url() . '.pdf',
              $params,
              'application/json'
          );
  
          return base64_decode($response->data->content);
      }
code: public function getInvoicePdf($letterId = null, $invoiceNo = null)
      {
          $params = array();
          if ($letterId)
              $params['letter_id'] = $letterId;
          if ($invoiceNo)
              $params['invoice_no'] = $invoiceNo;
  
          $response = $this->api->get(
              $this->url() . '.pdf',
              $params,
              'application/json'
          );
  
          return base64_decode($response->data->content);
      }
code_tokens: public function getInvoicePdf ( $ letterId = null , $ invoiceNo = null ) { $ params = array ( ) ; if ( $ letterId ) $ params [ 'letter_id' ] = $ letterId ; if ( $ invoiceNo ) $ params [ 'invoice_no' ] = $ invoiceNo ; $ response = $ this -> api -> get ( $ this -> url ( ) . '.pdf' , $ params , 'application/json' ) ; return base64_decode ( $ response -> data -> content ) ; }
docstring: Returns the PDF-file content for a specific billogram, invoice
  or letter document. Will throw a ObjectNotFoundError with message
  'Object not available yet' if the PDF has not yet been generated.
  
  @param null $letterId
  @param null $invoiceNo
  @return string
  @throws \Billogram\Api\Exceptions\ObjectNotFoundError
docstring_tokens: Returns the PDF - file content for a specific billogram invoice or letter document . Will throw a ObjectNotFoundError with message Object not available yet if the PDF has not yet been generated .