In order to turn it back on, all you need is to go to…
1. Click Microsoft Office icon. Click on ‘Words Options’.
2. Click on ‘Advanced’
3. Scroll down to look for ‘Display’
4. If you notice the options for the scroll bar are unchecked, you can “check” back the boxes.
5. Click OK. You will notice the scroll bar in Microsoft Words is reappearing back.