InvoiceController.php

            $pdfEngine = $this->container->get('knp_snappy.pdf');
            $response
                ->setContent($pdfEngine->getOutputFromHtml($html, [
                    'header-left' => 'nothing',
                    'header-center' => 'nothing again',
                    'header-html' => $this->admin->generateUrl('pdf-header', [], true)
                ]))
                ->headers->add([
                    'Content-Type'        => 'application/pdf',
                    'Content-Disposition' => 'attachment; filename="wyzbiz_invoice_' . $invoice->getInvoiceNumber() . '.pdf"'
                ]);