Revisions, history and comparisons
When you make changes to a document and then save it, the saved changes are stored as a revision. Revisions record the full history of the document from the moment it was created.
When you save a document, you will be prompted to enter a change record, for example, an explanation of why a particular change has been made. This information can be viewed and used later.
You can view a revision of a document by selecting it from the Revision list in the Document tab on the ribbon. When you select a revision, it opens into the document's tab with the revision name/number appearing in the tab's heading label. The content of a revision can be restored to the current ('Latest') revision (see Restore a revision). Revisions can only be viewed and not changed.
You can view a document's history, which is a list of the revisions and the changes that occurred in each revision. See View the document history.
Two revisions can be shown in side-by-side comparison in the Document Comparison window. See Compare revisions, versions and scenarios.