Unfortunately, documents are not something the plugin restricts because no PHP or WordPress script (to check for a logged-in WP user) run prior to loading the static files (.pdf, .doc, .jpg…etc). The web server just loads the file.
If you want to restrict access to the uploaded media files, you’ll have to configure your server to pass or “proxy” all requests to the uploads folder through a php script that can check if the user is logged-in.
Check out the following URL for an example of how to do this:
http://wordpress.stackexchange.com/a/37743/48165
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https://wordpress.org/support/topic/documents-not-protected/
