Format wars

With the release of Microsoft Office 2007, a new set of Office document file formats were introduced (docx, pptx, xlsx). If you have an older version of Office, it isn't compatible. You can't open the 2007 files in the older versions, which is why Office makes it possible to save the documents you create in the older document format. What's the point of having a new product though, if you can't use its new features?

Anyway, the point is this - sooner or later, you're going to start getting newer document formats from people and you may not have the Office version to use them. There are solutions. This page summarizes them nicely.