If you want to add calculator in Toolbar or menu do next:
1. Go to menu View,
2. In View menu go to Toolbar,
3. In Toolbar click on Customize,
4. When new window is open choose Commands,
5. In list of Categories go on Tools,
6. In list of Commands find Tools Calculate,
7. Click on Tolls Calculate and move him on Toolbar or in Drop Down menu,
8. When you drop Tools Calculate click on him whit right mouse button and choose "Change Button Image" from pop-up menu and choose icon for calculator,
9. From that same pop-up menu you can also precisely do you want that he show text, icon or both in toolbar,
10. Now type (example 2+2) in Word Document, mark it and click on calculator icon,
11. After that you will see result on status line in bottom of window.