Microsoft Word Preview 16.0.9226.2077 for Android - Download
Official Microsoft Word app for Android
It's important to note that Microsoft Word Preview has some significant requirements. To use it you'll need a device with at least a 7-inch screen, that runs Android 4.4 or higher, and that has at least 1 gigabyte of RAM. If your device doesn't meet any of these requirements you won't be able to use the app.
To edit text documents you just need to register in the app. If you're not logged in you'll only be able to open and view documents, but can't edit them. But if you log in you'll have at your disposal all the traditional Microsoft Word editing features.
Microsoft Word Preview is a polished application whose main drawback is that it only works on a limited range of devices. When it does work, though, it's an excellent app.