Thanks! It worked for string.php!
But now I got a new message:
Warning: Attempt to read property “ID” on null in /home/httpd/vhosts//wp-content/plugins/wp-download-codes/includes/shortcode.php on line 50 Warning: Undefined array key “yourcode” in /home/httpd/vhosts//wp-content/plugins/wp-download-codes/includes/shortcode.php on line 109 Warning: Undefined array key “yourcode” in /home/httpd/vhosts//wp-content/plugins/wp-download-codes/includes/shortcode.php on line 109