Did you know that Microsoft Word keeps many of the tracked changes and document history in the file in the form of embedded metadata? You can actually see these changes and editing history if you look for it.
"MS Word is well known for containing private information in file headers, but not any longer. Microsoft has released a tool to scrub leaky metadata from documents edited with its software. The Remove Hidden Data Add-In will permanently remove hidden and collaboration data, such as change tracking and comments, from MS Word, MS Excel, and MS PowerPoint files. For Office XP/Office 2003 only." Source TheRegister