Send attachments with PHP Mail()?

I agree with @MihaiIorga in the comments – use the PHPMailer script. You sound like you're rejecting it because you want the easier option. Trust me, PHPMailer is the easier option by a very large margin compared to trying to do it yourself with PHP's built-in mail() function. PHP's mail() function really isn't very good.

To use PHPMailer:

• Download the PHPMailer script from here: http://github.com/PHPMailer/PHPMailer
• Extract the archive and copy the script's folder to a convenient place in your project.
• Include the main script file -- require_once('path/to/file/class.phpmailer.php');

Now, sending emails with attachments goes from being insanely difficult to incredibly easy:

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$email = new PHPMailer();
$email->SetFrom('[email protected]', 'Your Name'); //Name is optional
$email->Subject   = 'Message Subject';
$email->Body      = $bodytext;
$email->AddAddress( '[email protected]' );

$file_to_attach = 'PATH_OF_YOUR_FILE_HERE';

$email->AddAttachment( $file_to_attach , 'NameOfFile.pdf' );

return $email->Send();

It's just that one line $email->AddAttachment(); -- you couldn't ask for any easier.

If you do it with PHP's mail() function, you'll be writing stacks of code, and you'll probably have lots of really difficult to find bugs.