An editor who is extremely close to me (my wife), after audibly gnashing her teeth in the upstairs office, shouted through the heater vent:
She: Gahh! I’ve just spent half an hour working on this Word document and I forgot to switch on Track Changes. Do I have to redo it?
Me: It depends. Are you working on a copy of the original document?
She: Of course. You think I’m an idiot?
Me: Banish the thought, my darling swottums! Your problems are over. With the document you’ve edited active, choose Tools -> Track Changes -> Compare Documents. In the Choose a File dialog box that appears, navigate to the original unedited document and click Open. A new document will appear with every change made between the two documents highlighted or, in Print Layout view, commented. All you have to do now is work on that new document and choose Tools -> Track Changes -> Highlight Changes and be sure that you’ve enabled the Track Changes While Editing option so that any changes you make from now on are also tracked.
She: You’ve earned your keep for another day.
Me: Thank you, dear.