This policy setting controls whether users can open documents (such as WordPerfect documents) that require the use of external converters that are installed with Word 2007.
If you enable this policy setting, users cannot open any files that require the use of a converter to open in Word 2007. 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 allows users to open any file for which an appropriate converter is installed.
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.