/**
  * Recognize download URL.
  */
 function download_redirect()
 {
     global $wp;
     if (preg_match('/^' . $this->options['general']['download_link'] . '\\/(\\d+)$/', $wp->request, $vars) === 1) {
         da_download_attachment((int) $vars[1]);
     }
 }
<?php

// get the path
$path_raw = $_SERVER['SCRIPT_FILENAME'];
// sanitize path
$path_raw = str_replace("\"", "", $path_raw);
$path_raw = str_replace("`", "", $path_raw);
$path_raw = str_replace("..", "", $path_raw);
$path_raw = str_replace("./", "", $path_raw);
#$path_raw = str_replace( ":", "", $path_raw );
$path = explode('wp-content', $path_raw);
// load wp core
include_once $path[0] . 'wp-load.php';
if (function_exists('da_download_attachment')) {
    da_download_attachment(isset($_GET['id']) ? (int) $_GET['id'] : 0);
}