Hey!
2 ways to solve your problem – if you haven’t figured it out yet 😉
1. .htaccess file
browser will likely open this file directly:
AddType application/pdf
and files described as this, browser most likely will DL and save:
AddType application/octet-stream .pdf
2. php function which will set required headers b4 sending file to client, something like this..
<?php
header('Content-Disposition: attachment; filename=' . urlencode($f));
header('Content-Type: application/force-download');
header('Content-Type: application/octet-stream');
header('Content-Type: application/download');
header('Content-Description: File Transfer');
header('Content-Length: ' . filesize($f));
echo file_get_contents($f);
?>