Click the Office button in the upper corner of the app.
At the bottom of the menu you should see "Word Options"  - click on that.
Switch to the Advanced tab
Scroll down to the "Show Document Content" area
You should find a dropdown list there for setting your Numeral shape to Hindi.

If you aren't seeing that control, you need to first enable Arabic in
Office.  Switch to the "Popular" tab and click the Language Settings button.  
Follow the directions in the language settings application to enable Arabic.