Document search. On the search page, there will be a document category to view. Similar to the "All" "News" "Images" "Video" categories. This category will sift through search results to include PDFs, Epubs, etc.
Additionally, there will be a report function that will enable users to report documents that have illegal content, or are illegal themselves. Of course, the report function isn't necessarily mandatory, but it will enable users to report content that they believe infringes upon their rights.

Thanks for reading my feature request/idea, and I hope you all liked it. :D