Send custom pdf in attachment in email in magento2.2.6

Question

How to add PDF as attachment in magento 2.2.6 ?

I have created code using an event "checkout_onepage_controller_success_action" to sends an email after place an order button click.

1) When someone clicks on the place order button then email sent successfully and redirect to the checkout/success page,

2) but when I use AddAttachment() function to send PDF as an attachment with email then after clicking on place order it's not redirecting to checkout/success/page and loader showing ... but I have received email with attachment in my mail

below is my code to add attachment :

 $this->inlineTranslation->suspend();
    $this->_transportBuilder
            ->setTemplateIdentifier($templateId)
            ->setTemplateOptions([
                'area' => $area,
                'store' => $store->getId()
            ])
            ->setTemplateVars($vars)
            ->setFrom($from)
            ->addTo($to['email'], $to['name'])
            ->addAttachment($pdfData, 'Credit Application');

    $transport = $this->_transportBuilder->getTransport();

    $transport->sendMessage();
    $this->inlineTranslation->resume(); 

//code to create PDF:

public function createPdf( $name,$email)
     {
                 $pdf = new \Zend_Pdf(); //Create new PDF file
                 $page = $pdf->newPage(\Zend_Pdf_Page::SIZE_A4);
                 $pdf->pages[] = $page;
                 $top = 810;
                 $left = 50;
                 $page->setFont(\Zend_Pdf_Font::fontWithName(\Zend_Pdf_Font::FONT_HELVETICA), 20);  //Set Font
                 $page->drawText("Heading", $left+200, $top-110,'UTF-8');

                 $page->setFont(\Zend_Pdf_Font::fontWithName(\Zend_Pdf_Font::FONT_HELVETICA), 14);  //Set Font
                 $page->drawText("Name : ".$name, $left, $top-140,'UTF-8');
                 $page->drawText("Email : ".$email, $left, $top-165,'UTF-8');

                 $pdfData = $pdf->render(); // Get PDF document as a string

                 header("Content-Disposition: inline; filename=result.pdf");

                 header("Content-type: application/x-pdf");
                 return $pdfData;
     }

Anyone has an idea then let me know.