The new default file formats in Office 2007 cannot be opened directly in older Office applications. Most enterprises upgrading to the new suite should initially standardize on the old formats to avoid leaving external users out in the cold.

Open XML

The new Office suite introduces Office Open XML, a royalty-free XML-based specification for electronic documents. Open XML formats have been implemented in the new versions of Word, Excel, and PowerPoint, but not in other Office 2007 applications.

While the older formats can still be opened in the new suite, the Open XML formats...