Since early November, an invite was required to use Office for Android on tablets. The invite-only stage is over and now Microsoft is casting a larger net for preview users. The only requirements are that the Android tablet runs KitKat or Lollipop and the display size sits between 7 and 10.1 inches. Does your tablet meet those requirements? Then head over to the Play Store and download Word, Excel, or PowerPoint. Microsoft would like to know the good and bad of its productivity suite on Android tablets, so be sure to let them know on Google+.
Source: Office Blogs