If you just need to view (not edit) documents, Office Documents Viewer is a free download that lets you read just about any sort of Office file. It's ad-heavy, but it certainly works in a pinch.
The most prominent aspect of the reader is that it sticks animated ads in any file you try to read with it. They usually don't get in the way, but it's still annoying. Office Documents Viewer displays text and HTML files smoothly, but it has to convert other files before they show up. This can take a long time if the file is huge. The app sports a plain interface that won't really excite you. It makes files easy to find and read, though. The fact that the app searches your SD card automatically helps, too. You can still look for files manually if you want.
It's about as much as you could ask for from a basic reader app. If you're not interested in an app that can help you actually edit Office files, this one is a quick, easy solution. Despite the ads, which are bad but could definitely be worse, Office Documents Viewer works well overall.