Files is the typical place where files (Word, PPT, etc) are stored. Libraries allow you to organize files and put some sharing restrictions on them.

I would create a Library and give all Chatter users (or public) access to it. Use that as the location for final, approved documents. Files would be the initial storage and would be used for development and discussions of documents until they are finalized. You may also want some Libraries for final documents that are internal only.

You can also use files and "share" specific files with a Chatter group. That would allow everyone in the Group to see the document and have access to it. It may be simpler to administer. You could have an "all users" group and place documents in there that are allowed to have widespread distribution.