When Microsoft originally released betas for Office for Android tablets, the company made the downloads available in more non-conventional means. Since the products were released as "Preview" (the apparent modern term for "beta"), Microsoft avoided making them available in the Google Play Store, and instead provided a special sign-up page. Later on, in November, that sign-up page was retired in lieu of a process where interested users had to join a special Google Plus group to get access to the downloads. At that time, the company promised an early 2015 release.
Today, Microsoft has fulfilled its promise and lifted the Google Plus group requirement, though you'll still want to use the group for providing feedback. Still in Preview, Word, Excel, and PowerPoint can now be downloaded directly from the Google Play store.
Here's the direct links:
