How do you compare two documents, to see changes, in word processing?

So I've got two documents with different names; one is an earlier version of the other one. Is there a tool that can do a comparison of the two documents, in which the word differences between the two documents (i.e. the updates) are highlighted? This way I can just review the changes, rather than having to read the entire 50 page document again.

(I feel like I've done this before, but I forget what the term for it is, so I'm having trouble searching for it).

Microsoft Works Word Processor and Google Document Editing are easily at hand, as tools. Thanks!