When working with files in an Office 365 site’s shared document library, you can see not only the current version of a file, but all the previous versions as well.
The dialog box shows all major and minor versions of the file, when they were created, and who created them. These files aren’t overwritten, so you can quickly see older versions.
Click the date/time for a version.
That version of the file opens in the program that it was created in. You can’t make changes to this version, but you can see how it looks and compare it to the current version.