As part of its continue investments in security Microsoft recently released the public preview (at the moment of this writing) of a new feature of the Azure Rights Management called Document Tracking.
In a few words sharing a document you can now “monitor the use, and thus abuse, of each of these documents shared using a variety of views. If the senders does not like what they see, they can (now) revoke access to the document regardless of where it is stored” (taken from http://blogs.technet.com/b/rms/archive/2015/05/04/doctracking.aspx).
Finally, I would like to remember that both AD RMS and Azure RMS can be configured as Information Rights Management system in SharePoint. If you are new to this topic you can take a look to this page to learn more.