If you open a study where you cannot make changes, the viewer opens in read-only mode. This applies when you open a study from a CD, do not have report editing privileges, or another user has the study open. When in read-only mode, a notification is displayed. The study can be observed, but no changes to the study will be recorded.
Some users may be given the ability to override read-only privileges. If so, a notification informs you of who currently controls the editable version of the study, and prompts you to break the lock. If you break the lock, you will have the only write-enabled copy of the study. The other user will be unable to save additional changes. Always notify the user listed in the notification you intend to break their lock.