From Office - Microsoft Edge Addons:
To get the extension, launch Microsoft Store > Click "Productivity" > type "Office browser extension" in the search box. More information here: Quick access to your Office files in the browser - Office Support
Office browser extension puts an icon on the Microsoft Edge toolbar that gives you direct access to your Office files, whether they are stored online or on your computer.
Office web extension can open files stored in OneDrive and OneDrive for Business.
You get the features of Word, Excel, PowerPoint, OneNote, and Sway right in your browser without needing Office installed.
The Office browser extension now includes proofing of your content*. It connects to a Microsoft online service that offers spelling, grammar and refinements suggestions for your writing on most websites and is available in more than 80 languages.
To get the extension, launch Microsoft Store > Click "Productivity" > type "Office browser extension" in the search box. More information here: Quick access to your Office files in the browser - Office Support