How do I create a wordpress site for sharing files?

I need to build a wordpress website for people to share written school tests they made. I do not want them to have access to admin back-end. They need to be able to register and upload the tests (pdf or jpg) from the front-end.
The material uploaded must be available to all registered users, with the possibility do password protect it.
Can you help me find a plugin for that? Nothing fancy or complex. I need something simple. Just a field for title, a field for content and a upload feature. And a register feature. And everything on the front-end.
Thanks,

Mauro