It does more than what you think!

My friend’s site had a problem. the customers of his site were not able to download the downloadable product links.
After clicking on the download link, the customer is redirected to an error page and the error was (Invalid download link. Go to shop).

So what was causing this problem? see the explanation from this page.

What is did do to solve this problem? I simply fix it by removing this plugin and installing this plugin.