Paper Access Permissions
All papers in your library are inaccessible to public.
All PDFs (and other attachments) in your library are inaccessible to public, or your friends. Only you can access the PDFs, figures, or other attachments.
By default, your friends can read your papers (only meta information, not PDFs or other attachments); However, if you set a paper to be private, then only you can access the paper. To change a paper to "private", select the paper, and check the box "Keep this paper or book private".