The Office Open XML Formats are based on XML and ZIP archive technologies. The new file format in Microsoft Office Word 2007 divides the file into document parts, each of which defines a part of the overall contents of the file. You can easily create, change, add, or delete data in a Word 2007 file programmatically or manually.
Nifty, huh? You can create and edit a Word 2007 document without opening Word. If you don't want to create a document from scratch but do want to see what's inside, take an existing Word 2007 file with a .DOCX extension and change the extension to .ZIP.
The July 2009 issue of LJN's Legal Tech Newsletter points out that this both good and bad for law firm IT departments. The Office Open XML Formats let other non-Microsoft data be stored in the file. However, this increases the chance that metadata and other information will inappropriately be shared with others. To find out how to protect yourself, see how to remove hidden data and personal information from Office documents.
And if you haven't heard of metadata before or are looking for more information about legal and ethical issues, check out The Posse List's E-discovery: Metadata grows in legal significance. - K