Attach pdf to custom email

Hello , i have this function who resent the woocommerce invoice to another email.

it work normally but without the attachement , i want to include the pdf attachement to it how i do it , i searched a lot but no hope

 <?php if (isset($_POST['submit'])) {
                function emailhtml( $order, $heading = false, $mailer ) {

                  $template = 'emails/invoice.php';

                return wc_get_template_html( $template, array(
               'order'         => $order,
              'email_heading' => $heading,
            'sent_to_admin' => false,
            'plain_text'    => false,
              'email'         => $mailer
             ) );
            
            }

          // load the mailer class
             $mailer = WC()->mailer();

            //format the email
            $recipient = $_POST['email'];
          $subject = __("Votre facture de chez viny culture!");
          $content = emailhtml( $order, $subject, $mailer );
         $headers = "Content-Type: text/html\r\n";
         //send the email through wordpress
         $mailer->send( $recipient, $subject, $content, $headers );
        }
?>

Thank you very much