javascript - PHP upload file to a contact form and email it

Question

I need to add in a contact form a section for people to upload their information (in PDF or image (JPG/PNG/ETC)). I got the section to upload the file, but it isn't sending the PDF with the e-mail (e-mail is working fine, but it arrives without the file uploaded, i don't know why). i will put my HTML/PHP code, so if you could help me it to know where is the problem or how can i achieve to upload a file, it would be great!

HTML

<form class="mb-2" action="freetest.php"  onsubmit="return validateForm();" method="post">
                <div class="form-group">
                    <div>
                        <label class="mb-0">Name</label>
                    </div>
                    <div class="form-group">
                        <input class="form-control-input" type="text" id="firstName" name="firstName" placeholder="Your Name" required>
                    </div>
                </div>

                <div class="form-group">
                    <div>
                        <label class="mb-0">Last Name</label>
                    </div>
                    <div class="form-group">
                        <input class="form-control-input" type="text" id="lastName" name="lastName" placeholder="Amelie" required>
                    </div>
                </div>

                <div class="form-group">
                    <div>
                        <label class="mb-0">Mail</label>
                    </div>
                    <div>
                        <input class="form-control-input" type="text" name="email" id="yourEmail" placeholder="[email protected]" required>
                    </div>
                </div>
                <div class=form-group>
                <label class="mb-0">?Any Question?</label>
                <textarea class="form-control-textarea" rows="8" name="message" required></textarea>
                </div>
                    <div class="form-group">
                        <div>
                            <label for="file-upload" class="custom-file-upload mt-2"><i class="fas fa-cloud-upload-alt"></i> Upload File</label>
                            <input id="file-upload" type="file" name="file" multiple="multiple" required>
                        </div>
                    </div>
                <button type="submit" class="btn-solid-lg">Send</button>
            </form>

PHP

 <?php
$ToEmail = '[email protected]'; 
        $EmailSubject = 'Free test'; 
        $mailheader = "From: ".$_POST["lastName"]."
"; 
        $mailheader .= "Reply-To: ".$_POST["email"]."
"; 
        $mailheader .= "Content-type: text/html; charset=iso-8859-1
"; 
        $MESSAGE_BODY = "First Name: ".$_POST["firstName"]."<br/>"; 
        $MESSAGE_BODY .= "Last Name: ".$_POST["lastName"]."<br/>"; 
        $MESSAGE_BODY .= "Email: ".$_POST["email"]."<br/>"; 
        $MESSAGE_BODY .= "Comment: ".nl2br($_POST["message"]).""; 
        mail($ToEmail, $EmailSubject, $MESSAGE_BODY, $mailheader) or die ("Failure");
?>

Answer 1

but it arrives without the file uploaded, i don't know why

I can tell you WHY:

You DO NOT ATTACH the file to the mail.

You only send text.

For some solutions how to do this please visit this thread which will explain how to do this with and without phpmailer

Send attachments with PHP Mail()?