How to fix PDF Attachment Not Working Issue in Magento 2.3.3

Emails are one of the traditional & cheapest ways to send updates to the customers. Today, almost every CMS provides the functionality to engage and stay connected with users via emails. And Magento does the same and provides an email automation system that notifies store customers every time their order status gets updated or changed. Taking it to the next level, Magento also generates and sends order doc PDFs as an email attachment to the customers. So they can have virtual docs of their purchase.
But with the update to Magento 2.3.3, many Magento 2 store owners are facing an issue while sending PDF as an email attachment. It seems like there an issue in their core and one needs to fix it so all the store owners can fix and continue to use their upgraded Magento 2.3.3. So, if you are in search of fixing a PDF attachment issue, your search ends here. Just follow these steps and your email attachment will start working like charm as it worked previously.
First, you need to create “di.xml” file inside your extension folder.
app/code/VENDOR/EXTENSION/etc/

<pre class="lang:default decode:true">
<preference for="\Magento\Framework\Mail\Template\TransportBuilder" type="VENDOR\EXTENSION\Model\Mail\Template\TransportBuilder" />
</pre>

Now, you have to create one more file “transportBuilder.php” inside your template folder with below code.
app/code/VENDOR/EXTENSION/model/mail/template/

<pre class="lang:default decode:true">
<?php
declare(strict_types=1);
namespace VENDOR\EXTENSION\Model\Mail\Template;
use Magento\Framework\App\TemplateTypesInterface;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\Exception\MailException;
use Magento\Framework\Mail\EmailMessageInterface;
use Magento\Framework\Mail\EmailMessageInterfaceFactory;
use Magento\Framework\Mail\AddressConverter;
use Magento\Framework\Mail\Exception\InvalidArgumentException;
use Magento\Framework\Mail\MessageInterface;
use Magento\Framework\Mail\MessageInterfaceFactory;
use Magento\Framework\Mail\MimeInterface;
use Magento\Framework\Mail\MimeMessageInterfaceFactory;
use Magento\Framework\Mail\MimePartInterfaceFactory;
use Magento\Framework\Mail\Template\FactoryInterface;
use Magento\Framework\Mail\Template\SenderResolverInterface;
use Magento\Framework\Mail\TemplateInterface;
use Magento\Framework\Mail\TransportInterface;
use Magento\Framework\Mail\TransportInterfaceFactory;
use Magento\Framework\ObjectManagerInterface;
use Magento\Framework\Phrase;
use Zend\Mime\Mime;
use Zend\Mime\PartFactory;

/**
 * TransportBuilder
 *
 * @api
 * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
 * @since 100.0.2
 */
class TransportBuilder extends \Magento\Framework\Mail\Template\TransportBuilder
{
    /**
     * Template Identifier
     *
     * @var string
     */
    protected $templateIdentifier;

    /**
     * Template Model
     *
     * @var string
     */
    protected $templateModel;

    /**
     * Template Variables
     *
     * @var array
     */
    protected $templateVars;

    /**
     * Template Options
     *
     * @var array
     */
    protected $templateOptions;

    /**
     * Mail Transport
     *
     * @var TransportInterface
     */
    protected $transport;

    /**
     * Template Factory
     *
     * @var FactoryInterface
     */
    protected $templateFactory;

    /**
     * Object Manager
     *
     * @var ObjectManagerInterface
     */
    protected $objectManager;

    /**
     * Message
     *
     * @var EmailMessageInterface
     */
    protected $message;

    /**
     * Sender resolver
     *
     * @var SenderResolverInterface
     */
    protected $_senderResolver;

    /**
     * @var TransportInterfaceFactory
     */
    protected $mailTransportFactory;

    /**
     * Param that used for storing all message data until it will be used
     *
     * @var array
     */
    private $messageData = [];

    /**
     * @var EmailMessageInterfaceFactory
     */
    private $emailMessageInterfaceFactory;

    /**
     * @var MimeMessageInterfaceFactory
     */
    private $mimeMessageInterfaceFactory;

    /**
     * @var MimePartInterfaceFactory
     */
    private $mimePartInterfaceFactory;

    /**
     * @var AddressConverter|null
     */
    private $addressConverter;

    protected $attachments = [];

    protected $partFactory;

    /**
     * TransportBuilder constructor
     *
     * @param FactoryInterface $templateFactory
     * @param MessageInterface $message
     * @param SenderResolverInterface $senderResolver
     * @param ObjectManagerInterface $objectManager
     * @param TransportInterfaceFactory $mailTransportFactory
     * @param MessageInterfaceFactory|null $messageFactory
     * @param EmailMessageInterfaceFactory|null $emailMessageInterfaceFactory
     * @param MimeMessageInterfaceFactory|null $mimeMessageInterfaceFactory
     * @param MimePartInterfaceFactory|null $mimePartInterfaceFactory
     * @param addressConverter|null $addressConverter
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     * @SuppressWarnings(PHPMD.ExcessiveParameterList)
     */
    public function __construct(
        FactoryInterface $templateFactory,
        MessageInterface $message,
        SenderResolverInterface $senderResolver,
        ObjectManagerInterface $objectManager,
        TransportInterfaceFactory $mailTransportFactory,
        MessageInterfaceFactory $messageFactory = null,
        EmailMessageInterfaceFactory $emailMessageInterfaceFactory = null,
        MimeMessageInterfaceFactory $mimeMessageInterfaceFactory = null,
        MimePartInterfaceFactory $mimePartInterfaceFactory = null,
        AddressConverter $addressConverter = null
    ) {
        $this->templateFactory = $templateFactory;
        $this->objectManager = $objectManager;
        $this->_senderResolver = $senderResolver;
        $this->mailTransportFactory = $mailTransportFactory;
        $this->emailMessageInterfaceFactory = $emailMessageInterfaceFactory ?: $this->objectManager
            ->get(EmailMessageInterfaceFactory::class);
        $this->mimeMessageInterfaceFactory = $mimeMessageInterfaceFactory ?: $this->objectManager
            ->get(MimeMessageInterfaceFactory::class);
        $this->mimePartInterfaceFactory = $mimePartInterfaceFactory ?: $this->objectManager
            ->get(MimePartInterfaceFactory::class);
        $this->addressConverter = $addressConverter ?: $this->objectManager
            ->get(AddressConverter::class);
        $this->partFactory = $objectManager->get(PartFactory::class);
        parent::__construct($templateFactory, $message, $senderResolver, $objectManager, $mailTransportFactory, $messageFactory, $emailMessageInterfaceFactory, $mimeMessageInterfaceFactory,
            $mimePartInterfaceFactory, $addressConverter);
    }

    /**
     * Add cc address
     *
     * @param array|string $address
     * @param string $name
     *
     * @return $this
     */
    public function addCc($address, $name = '')
    {
        $this->addAddressByType('cc', $address, $name);

        return $this;
    }

    /**
     * Add to address
     *
     * @param array|string $address
     * @param string $name
     *
     * @return $this
     * @throws InvalidArgumentException
     */
    public function addTo($address, $name = '')
    {
        $this->addAddressByType('to', $address, $name);

        return $this;
    }

    /**
     * Add bcc address
     *
     * @param array|string $address
     *
     * @return $this
     * @throws InvalidArgumentException
     */
    public function addBcc($address)
    {
        $this->addAddressByType('bcc', $address);

        return $this;
    }

    /**
     * Set Reply-To Header
     *
     * @param string $email
     * @param string|null $name
     *
     * @return $this
     * @throws InvalidArgumentException
     */
    public function setReplyTo($email, $name = null)
    {
        $this->addAddressByType('replyTo', $email, $name);

        return $this;
    }

    /**
     * Set mail from address
     *
     * @param string|array $from
     *
     * @return $this
     * @throws InvalidArgumentException
     * @see setFromByScope()
     *
     * @deprecated 102.0.1 This function sets the from address but does not provide
     * a way of setting the correct from addresses based on the scope.
     */
    public function setFrom($from)
    {
        return $this->setFromByScope($from);
    }

    /**
     * Set mail from address by scopeId
     *
     * @param string|array $from
     * @param string|int $scopeId
     *
     * @return $this
     * @throws InvalidArgumentException
     * @throws MailException
     * @since 102.0.1
     */
    public function setFromByScope($from, $scopeId = null)
    {
        $result = $this->_senderResolver->resolve($from, $scopeId);
        $this->addAddressByType('from', $result['email'], $result['name']);

        return $this;
    }

    /**
     * Set template identifier
     *
     * @param string $templateIdentifier
     *
     * @return $this
     */
    public function setTemplateIdentifier($templateIdentifier)
    {
        $this->templateIdentifier = $templateIdentifier;

        return $this;
    }

    /**
     * Set template model
     *
     * @param string $templateModel
     *
     * @return $this
     */
    public function setTemplateModel($templateModel)
    {
        $this->templateModel = $templateModel;
        return $this;
    }

    /**
     * Set template vars
     *
     * @param array $templateVars
     *
     * @return $this
     */
    public function setTemplateVars($templateVars)
    {
        $this->templateVars = $templateVars;

        return $this;
    }

    /**
     * Set template options
     *
     * @param array $templateOptions
     * @return $this
     */
    public function setTemplateOptions($templateOptions)
    {
        $this->templateOptions = $templateOptions;

        return $this;
    }

    /**
     * Get mail transport
     *
     * @return TransportInterface
     * @throws LocalizedException
     */
    public function getTransport()
    {
        try {
            $this->prepareMessage();
            $mailTransport = $this->mailTransportFactory->create(['message' => clone $this->message]);
        } finally {
            $this->reset();
        }

        return $mailTransport;
    }

    /**
     * Reset object state
     *
     * @return $this
     */
    protected function reset()
    {
        $this->messageData = [];
        $this->templateIdentifier = null;
        $this->templateVars = null;
        $this->templateOptions = null;
        return $this;
    }

    /**
     * Get template
     *
     * @return TemplateInterface
     */
    protected function getTemplate()
    {
        return $this->templateFactory->get($this->templateIdentifier, $this->templateModel)
            ->setVars($this->templateVars)
            ->setOptions($this->templateOptions);
    }

    /**
     * Prepare message.
     *
     * @return $this
     * @throws LocalizedException if template type is unknown
     */
    protected function prepareMessage()
    {
        $template = $this->getTemplate();
        $content = $template->processTemplate();
        switch ($template->getType()) {
            case TemplateTypesInterface::TYPE_TEXT:
                $part['type'] = MimeInterface::TYPE_TEXT;
                break;

            case TemplateTypesInterface::TYPE_HTML:
                $part['type'] = MimeInterface::TYPE_HTML;
                break;

            default:
                throw new LocalizedException(
                    new Phrase('Unknown template type')
                );
        }
        $mimePart = $this->mimePartInterfaceFactory->create(['content' => $content]);
        $parts = count($this->attachments) ? array_merge([$mimePart], $this->attachments) : [$mimePart];
        $this->messageData['body'] = $this->mimeMessageInterfaceFactory->create(
            ['parts' => $parts]
        );

        $this->messageData['subject'] = html_entity_decode(
            (string)$template->getSubject(),
            ENT_QUOTES
        );
        $this->message = $this->emailMessageInterfaceFactory->create($this->messageData);

        return $this;
    }

    /**
     * Handles possible incoming types of email (string or array)
     *
     * @param string $addressType
     * @param string|array $email
     * @param string|null $name
     *
     * @return void
     * @throws InvalidArgumentException
     */
    private function addAddressByType(string $addressType, $email, ?string $name = null): void
    {
        if (is_string($email)) {
            $this->messageData[$addressType][] = $this->addressConverter->convert($email, $name);
            return;
        }
        $convertedAddressArray = $this->addressConverter->convertMany($email);
        if (isset($this->messageData[$addressType])) {
            $this->messageData[$addressType] = array_merge(
                $this->messageData[$addressType],
                $convertedAddressArray
            );
        }
    }

    /**
     * @param string|null $content
     * @param string|null $fileName
     * @param string|null $fileType
     * @return TransportBuilder
     */
    public function addAttachment(?string $content, ?string $fileName, ?string $fileType)
    {
        $attachmentPart = $this->partFactory->create();
        $attachmentPart->setContent($content)
            ->setType($fileType)
            ->setFileName($fileName)
            ->setDisposition(Mime::DISPOSITION_ATTACHMENT)
            ->setEncoding(Mime::ENCODING_BASE64);
        $this->attachments[] = $attachmentPart;

        return $this;
    }
}
</pre>

Lastly, we have create a call to the file as shown below.

<pre class="lang:default decode:true">
$this->transportBuilder->addAttachment($content, $fileName, 'application/pdf');
</pre>

That’t it. Now your email attachment issue is resolved. You are free to manipulate this code according to your need.
Lastly, if you found this blog helpful, don’t forget to share it with your colleagues and Magento Friends and Let us know if you are facing any issue while implementing this code.
Happy Coding!