If you already have a Google account you could also use Google Drive to sync your documents to the cloud then using the Google Drive app you can even edit the documents on any device. Depending on the complexity of the document the conversion is pretty simple.
I bought an app from the app store, called "Pages", for about $10. I know, it is a little pricey but it allows me to not only view my MS Office files but also to edit and even create them as well. The app is supplied by Apple Inc. and works very well. I am generally one who uses the free apps or 99 centers but I just couldn't find anything to meet my needs at a free or lower price level.