Word: View two parts of document at once

With the file open, click on the small horizontal line above the Ruler toggle, or simply press Ctrl-Alt-S. A line will appear, bisecting the screen. Above and below, you'll see the active document; you can scroll in each section independently to edit in different areas while viewing others. You can even change the view, for example from Print Layout to Draft.
The dividing line can be moved up and down on the screen, and you can get rid of it by pressing the same button you used to activate it, pressing Ctrl-Alt-S again, or grabbing it with your mouse and moving it all the way to either the top or bottom of the window.