How can I attach files to a Contact Us form?

Question

I am trying to create a contact us form with the following fields and file attachments on Magento 2.3.2:

<?php
// @codingStandardsIgnoreFile

?>
<?php 
    $themeHelper = $this->helper('MGS\Mpanel\Helper\Data');
    $canUsePanel = $themeHelper->acceptToUsePanel();
?>
<div class="contact-form-content">
    <div class="row">
        <div class="col-sm-6 col-xs-12 margin-bottom60">
            <!-- Static block contact_page_custom_block -->
            <p>Nav goes here </p>
        </div>
        <div class="col-sm-6 col-xs-12 margin-bottom60">
            <h3 class="text-uppercase margin-bottom15"><?php echo __('Send us a message'); ?></h3>
            <form class="form contact" action="<?php /* @escapeNotVerified */ echo $block->getFormAction(); ?>" id="contact-form" method="post" data-hasrequired="<?php /* @escapeNotVerified */ echo __('* Required Fields') ?>" data-mage-init='{"validation":{}}'>
                <fieldset>
                    <div class="form-group name required">
                        <label for="name"><?php echo __('First Name'); ?></label>
                        <input name="name" id="name" title="<?php /* @escapeNotVerified */ echo __('First Name') ?>" value="<?php echo $block->escapeHtml($this->helper('Magento\Contact\Helper\Data')->getUserName()) ?>" class="input-text form-control" type="text" data-validate="{required:true}"/>
                    </div>
                    <div class="form-group name required">
                        <label for="name"><?php echo __('Last Name'); ?></label>
                        <input name="name" id="name" title="<?php /* @escapeNotVerified */ echo __('Last Name') ?>" value="" class="input-text form-control" type="text" data-validate="{required:true}"/>
                    </div>
                </fieldset>
                <div class="form-group email required">
                    <label for="email"><?php echo __('Email'); ?></label>
                    <input name="email" id="email" title="<?php /* @escapeNotVerified */ echo __('Email') ?>" value="<?php echo $block->escapeHtml($this->helper('Magento\Contact\Helper\Data')->getUserEmail()) ?>" class="input-text form-control" type="email" data-validate="{required:true, 'validate-email':true}"/>
                </div>
                <div class="form-group topic required">
                    <label for="topic"><?php /* @escapeNotVerified */ echo __('Topic') ?></label>
                    <select name="topic" id="topic">
                        <option value="selected">Select a Topic</option>
                        <option name="items" value="Items">Items</option>
                        <option name="shpping" value="Shipping">Shipping</option>
                    </select>
                </div>
                <div class="form-group comment required">
                    <label for="comment"><?php echo __('Message'); ?></label>
                    <textarea name="comment" id="comment" title="<?php /* @escapeNotVerified */ echo __('Content') ?>" class="input-text form-control" cols="5" rows="7" data-validate="{required:true}"></textarea>
                </div>
                <div class="field attachment-pdf required">
                    <label class="label" for="attachment-pdf"><span><?php /* @escapeNotVerified */ echo __('PDF') ?></span></label>
                    <div class="control">
                        <input name="attachment-pdf" id="attachment-pdf" accept="pdf/*" name="attachment-pdf" type="file" value="" />
                    </div>
                </div>
                <div class="field attachment-image required">
                    <label class="label" for="attachment-image"><span><?php /* @escapeNotVerified */ echo __('Image') ?></span></label>
                    <div class="control">
                        <input name="attachment-image" id="attachment-image" accept="image/*" name="attachment-image" type="file" value="" />
                    </div>
                </div>
                <?= $block->getChildHtml('form.additional.info') ?>
                <div class="actions-toolbar">
                    <input type="hidden" name="hideit" id="hideit" value="" />
                    <button type="submit" title="<?php /* @escapeNotVerified */ echo __('Send Messages') ?>" class="action submit btn btn-primary">
                        <span><?php /* @escapeNotVerified */ echo __('Send Messages') ?></span>
                    </button>
                </div>
            </form>
        </div>
    </div>
    
</div>

But I cannot find a comprehensive guide, most are either super old or lack key information. Ideally I would like to extend the Magento core module Magento_Contact. I was trying to follow this guide but on step two I don't really understand where I am supposed to put the files

Can someone please help me? I don't know why I am struggling with something so basic.

I am trying to use DominicWatts's ContactAttachment but I get the following error on form submit.

Fatal error: Uncaught Error: Call to undefined method Mageplaza\Smtp\Helper\Data::versionCompare() in /var/www/html/app/code/Mageplaza/Smtp/Mail/Transport.php:157 Stack trace: #0 /var/www/html/app/code/Mageplaza/Smtp/Mail/Transport.php(111): Mageplaza\Smtp\Mail\Transport->getMessage(Object(Magento\Email\Model\Transport\Interceptor)) #1 /var/www/html/vendor/magento/framework/Interception/Interceptor.php(135): Mageplaza\Smtp\Mail\Transport->aroundSendMessage(Object(Magento\Email\Model\Transport\Interceptor), Object(Closure)) #2 /var/www/html/vendor/dotmailer/dotmailer-magento2-extension/Plugin/TransportPlugin.php(75): Magento\Email\Model\Transport\Interceptor->Magento\Framework\Interception\{closure}() #3 /var/www/html/vendor/magento/framework/Interception/Interceptor.php(135): Dotdigitalgroup\Email\Plugin\TransportPlugin->aroundSendMessage(Object(Magento\Email\Model\Transport\Interceptor), Object(Closure)) #4 /var/www/html/vendor/magento/module-email/Model/Mail/TransportInterfacePlugin.php(48): Magento\Email\Model\Transpor in /var/www/html/app/code/Mageplaza/Smtp/Mail/Transport.php on line 157

Answer 1

I created extension which does this

https://github.com/DominicWatts/ContactAttachment