Press Shift+F5 one, two, or three times. A fourth press takes you back to the position from which you started.
When you close a document, Word stores only the last editing location, not the last three; so when you reopen the document, you can use Shift+F5 only once to return to the last editing location. Because of the way that Word close files when you exit, Word may not save the last editing location in some files. However, if you close your files manually before exiting Word, it will always save the last editing location.
Note: If multiple documents are open and editing last occurred in a document that’s not onscreen, Shift+F5 will take you there.
You can also use the Shift+F5 keyboard shortcut to deselect a block of text and returns to the text you were editing before making the selection.