Toward the editing process with my agent, we'd all read my book more times than we care to count. You simply can't see the words after a certain point. Finally the time came, on draft 8 when she wanted to do one last pass of the manuscript. The trick? She only wanted to see the new material and I had already accepted the changes in the document.
The answer? The Compare Document feature in Word.
Open your original document (For me, draft 7 of 8)
Under tools, select Track Changes--> Compare Document
Select the documents you wish to compare. Make sure your older draft is selected as the original document and the newer draft as the revised document.
You should have a 3rd document that shows all changes between Version 1 and Version 2 of your document. Make sure to title it with a distinct title so you don't overwrite either version.
Voila! You can easily see the changes between your documents without using one of the online services that requires you to upload your precious manuscript and you've just saved yourself or someone else hours of reading.
Hope this helps!