What you want to achieve will not involve only client-side code, but server side code too..
I´m not giving you 100% solution, you will have to do some extra work(you will need a mechanism to validate the url that I cannot guess by myself without knowing how do you validate users), but this will point you the way:
Make a PHP File to handle file download this way
$crypted_url = $_GET["url_to_file_encripted_somehow"];
$file_path = get_file_path_from_crypted_url($crypted_url);
if ( $file_path === false ){
include "403.html";
die;
}
$filename = "whatever";
header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=$filename.".pathinfo($file_path, PATHINFO_EXTENSION));
echo readfile($documento->link_archivo());
I may be of further help if you explain the mechanism you want to use to validate the user.