What is version history in Office 365?
Word stores a version history of most files saved to OneDrive. Version history can allow you to recover lost drafts or undo large edits. Version history saves a copy every time you close a file and keeps that save for 30 days. You can access a documents version history by following the steps below.
Click on the title at the top of the screen (in this image, Trees2).
It will bring up a menu that looks like this. Click Version History.
You will see this sidebar showing all the versions of the document.
Click Open Version for the version you want to open and it will open the file. You can then either save the file as normal or click restore, which will overwrite your current file.