Need help finding the right password protect plugin

What plugins should I consider to password protect a single site page and documents with Username and Password, where it handles the signup process and forgotten passwords automatically? I don’t think I want a WordPress username and password for this – I don’t want to give users access to the WP backend. I also want to secure the documents, so users cannot access them simply by typing in the document url to get around the securities. Is there such a plugin somewhere?

Thank you for your help!