It is very useful in case you receive files created using Microsoft word and you don't have it installed. This is much lighter than the complete version and is free and allows you to view all those files.
It includes all necessary tools to view Microsfot Word files and it also allows you to copy, search for words or print it.
By this way, you will not have to use the complete version of Microsoft Word if you can't afford it.
Decide the way you want to view the document: Regular, web, print view, read view and outline.
The interface is based on Microsoft Word 2003, but it is also compatible with files created using Office 2007.