It is called "read-Only" mode. A module box will display, saying it is already opened by another user, and it will tell you who is editing it. It then will ask you if you wish to notified upon closing, or open a READ-Only copy. Choose "notify", as READ-ONLY will allow you to only veiw. It will discard any changes upon closing.
"If you can't soar with the eagles, then don't fly with the flock!" - Oliver Sykes; Bring Me The Horizon