You may need to install or reinstall Office from the Microsoft Store app if, for example, you have a computer running Windows 10 S (including some Surface Laptops).
INSTALL AND ACTIVATE OFFICE THE FIRST TIME ON A NEW PC RUNNING WINDOWS 10 S
If you have a computer running Windows 10 S (including Surface Laptop) and you haven't installed Office yet, do the following:
Go to Start , scroll through the App List and select an Office app such as Word, Excel, or PowerPoint. The Microsoft Store app opens.
If you're not already signed in to the Store with a Microsoft account, sign in now. If you don't have an account, create one. This is the account that will be associated with Office and is what you'll use anytime you want to install or reinstall Office.
The Office page in the Microsoft Store opens.
Select Install. A notification appears in the lower-right corner after each app finishes installing.
Open an Office app by selecting one of the app tiles, such as Word or Excel on the Office product page. An Office window opens telling you what apps are included in the version of Office you just installed.
Select Got it! You can now start using Office.