How to Open Office 2007 files in earlier versions of Office and vise versa

you can open earlier office files in office 2007 without any problem. You dont need to do any thing.
To open Office 2007 files in older version of office you need to install the Microsoft Office Compatibility Pack for 2007 Office Word, Excel and PowerPoint File Formats and any necessary Office updates. By using the Compatibility Pack for the 2007 Office system, you can open, edit some items, and save Office Word 2007 documents in previous versions of Word.

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