Share documents and references with small teams. You have to be invited to these groups and they allow you to share PDFs and collaborate using shared annotations.
PDFs opened from a private group will be marked with '(Shared)' in the reading tab. This will help you differentiate between a shared PDF and one from your personal library.
There are two types of public groups in Mendeley Reference Manager: open public groups and invite-only public groups.
Open public groups can be joined by anyone with a Mendeley account, whereas you must first be invited by one of the members of an invite-only group to join.
Both public group types can be used to share references with other members of the group. Neither allow the sharing of PDFs.