Document presence lets you see who is looking at a document. You can see document presence information in your list of contacts, in the Social Bar under Trending, on a profile page, and in someone's activity status in the item's membership bar.
Document presence information also appears above a document preview, where the profile picture of everyone who is looking at a document appears. You can click a profile picture in this row to see options for co-browsing with this person, opening a One-on-One Conversation with them, or navigating to their profile.