Now when you open a shared Doc file in Google Drive, you'll see the profile photos of other viewers and collaborators, (if they have an active Google+ profile) at the top right of the page, making it easy for you to do a quick scan of who is in the file.
You can hover over a photo to see details about the viewer and even add them to your circles in Google+. In addition, you are able to chat with a group of viewers making it easy for you to quickly message everyone who is in the file.
To watch a short demo about this new chat and photo profile feature in Google Drive, take a look at this VIDEO by Google Gooru.