This policy setting controls whether Word 2007 users can open binary files that were saved in pre-release versions of Word.
If you enable this policy setting, Word 2007 users will not be able to open binary Word documents saved with pre-release versions of Word. This setting can be used to guard against theoretical future zero-day attacks that target specific file types.
If you disable or do not configure this policy setting, Word 2007 users can open Word binary files (.doc and .dot) that were saved in Beta or pre-release versions of Word, including pre-release versions of Word 2007.
Note - See Plan block file format settings in the 2007 Office system (http://r.office.microsoft.com/r/rlidGroupPolicyBlockFileForm2?clid=en-us) in the 2007 Office Resource Kit for more information about using Group Policy to manage and enforce file format requirements. Also, see the "File Block Technology" section in Chapter 4 of the 2007 Microsoft Office Security Guide for information about the Microsoft Office Isolated Conversion Environment (MOICE), which provides another method.