Office Editing is a free Chrome extension from Google which enables users to view and edit Microsoft Word, Excel, and PowerPoint files in Google Docs, Sheets, and Slides.
The extension doesn't add yet another icon to your address bar. Instead, simply drag and drop an Office file into Chrome (even if you're offline), or open one in Gmail or Drive, and it'll be opened in Docs, Sheets or Slides.
This works just fine as a viewer, or you're able to carry out some very basic editing operations, then save the file in its original format.
If you need more then you can switch to Docs, Sheets or Slides and edit the document as normal.
Office Editing for Chrome worked reasonably well for us, but editing features are basic, and there are a lot of Chrome Store reviews questioning its reliability.