Instead of opening Windows calculator to perform a calculation utilized in a Word document, use the built-in calculator function in Word. Go to View -> Toolbars -> Customize and select “Tools” under “Categories.” Click on the “Tools Calculate” button and drag it to where you desire on your toolbar. Close the dialogue box. The calculator is now installed. To use it, simply highlight any calculation and press “Tools Calculate.” The result of the calculation is automatically saved to the clipboard, so a Paste or Ctrl +V would do the trick.