It is possible to open Microsoft Office documents with another Office version (for example an .xlsx file with Microsoft Office 2003), by using a compatibility plug-in.

Click on the following link to go to the official Microsoft Office website. Here you can find more information and download the plug-in.

http://office.microsoft.com/en-gb/help/introduction-to-new-file-name-extensions-HA010006935.aspx#BM2