Locking down Office documents isn't new, but Office 2010 offers a quicker, more informal method to discourage editing once a document is finished: You can mark it as final.
This does away with the need to create and remember a password or set complicated permissions. It won't prevent editing or copying if a teammate or customer wants to do so, but it can send a signal that the document is done and requires no further tweaking.
To mark a document as final, go to the File tab, click Protect Document, and select Mark as Final:
You can see the Restrict Editing and Restrict Permission by People options if you need stricter enforcement. Once you choose Mark as Final, you have one more chance to back out (though it's easy enough to reverse if you change your mind later):
Click OK if you're sure. Now, when you or anyone else opens the document, this banner appears across the top:
Simply click the Edit Anyway button, and the document reverts back to a working draft.