Microsoft indicates at http://www.microsoft.com/en-us/download/details.aspx?id=3, "Install this compatibility pack if you would like to open, edit, and save documents, workbooks, and presentations that were created in the newer versions of Word, Excel, and PowerPoint."
My installation of the Word Viewer tries to update when it detects newer file formats, but fails. The Viewer can currently be downloaded from http://www.microsoft.com/en-us/download/details.aspx?id=4.
