Google is enabling the sharing of links to any Drive file directly from the chat window in Hangouts. The shared link will show a preview of the file inside the chat window, even when other participants don't have their chat window open. When a user clicks on a shared link, the file will open in a different browser tab making it easier to work on the file in full view. To share a link from Drive during a Hangouts video call, click on the Chat icon and then click the Google Drive picker icon from within the chat window.
Note that the Google Drive Hangouts App will no longer be available after December 15, 2014. For more information, see Better Collaboration in Hangout Video Calls.