download-file-browser.php

global $user;
$file = new stdClass();
$file->fid = NULL;
$file->uri = 'private://' . $filename;
$file->filename = $filename;
$file->filemime = file_get_mimetype($file->uri);
$file->uid = $user->uid;
$file->status = 0;

file_save($file);
$headers = file_get_content_headers($file);
$headers['Content-Disposition'] = 'attachment; filename="' . $filename . '"';
file_transfer($file->uri, $headers);