public function showFileAction()
    {
        $id = $this->getRequest()->get($this->admin->getIdParameter());
        $invoice = $this->admin->getObject($id);

        if (!$invoice) {
            throw $this->createNotFoundException(sprintf('Unable to find the invoice with id : %s', $id));
        }

        $this->admin->checkAccess('show', $invoice);

        return new Response(
            $invoice->getFile(),
            200,
            ['Content-Type' => 'application/pdf']
        );
    }