Yes, you can edit Office Files in OnBase.  

When you Retrieve (find) a document in OnBase, click on it to open the document. 

It opens in the associtated application associated inside an OnBase window.  You can use all of the native application's tools.

Note: For this to work correctly Microsoft has to be configured with the following settings:

 File | Options | General | from there you should see two option one says "optimize for best appearance" and "optimize for compatibility" you'll want to make sure "optimize for compatibility" is checked.