Jerry,
You can re-install the only things which will be replaced will be the program files and not the files you created with it.
You "may" be able to choose "repair" when you go to correct your problems. I can not remember if all versions of Office allow you to do that..
I would expect that your files ( your word documents ) are in a folder such as "My Documents" or some other folder.The program files are normally in the Program files folder far away from anything the program would write to. Back ups to important documents are always important, and to be honest I always tell people DVD's or CD's. and then for really important documents and pictures... more then one copy. I have 3 portable drives, each one carries copies of the others. I have seen too many bad things happen.
Curt