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It should be noted at docx, xlsx, pptx, etc are the defaults for Office 2007 and later. For users without the compatibility pack (or for users who are using a different Word Processor such as Pages or Open Office), docx files can be opened in a web browser. xlxs files may get corrupted or generally not appear as intended when translating in html. It is recommended, thus, that users save their work using the traditional file extensions (doc, xls, ppt, etc)of Office 2003/2004 install the compatibility pack.
Other Versions
Office 2003 and 2004
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