I recently ran into an issue with an e-mail attachment. The extension of the attachment was .xlsx, which made me believe that it was a Microsoft Excel document. I saved the document to the local hard drive and attempted to open it, but was dismayed to find that no application was associated with it.
After looking online to find the application associated with the extension I found out that it was indeed an Excel file for Microsoft Office 2007. I had Office 2000 installed, which explains why I couldn’t open it. After some more research I found out that there is a tool you can download and install that will allow older versions of the Office tools to open files from newer versions.