User only downloadable files

I’m a newbie at WordPress so maybe I missed this lesson. Some of my blog is available to registered users only, including a page that has links to downloadable pdf and word documents.

I secured the page by adding php code as described in Members only sections

This works fine, but if the file URL is entered directly in the browser, it can be downloaded. How do I make the file secure, and accessible only through the registered user page?

I put the files in public_html/wp_content/uploads folder. Is that correct?