Kingsoft Office is free and can read and edit MS office files. There is also Officesuite though I have not used it.
If you are rooted Stickmount will read a usb connected to the Nexus. There is another app if you are not rooted.
There are many file managers, most are free. The ones I like best are "ES Explorer" which will even let you move files from your pc via wifi, and Root Explorer. But there are many others.
Hope this helps.
Sent from my Nexus 7