Kentico CMS provides you with the option to rollback to previous version and add comments.
Note: Once you rollback to a previous version and you save, a newer version will be added, even if no changes are made.
In order to work with the properties of a document you must be in the Properties Tab, and Versions Sub menu
You can do two things from this window:
View Version Information by clicking on the Version button
Roll Back to an older version by clicking on the Roll back button