Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats

Suppose you have a colleague or friend who has installed Microsoft Office 2007, and sends you documents generated from that software, the default file created will not be readable in earlier versions of the software such as Office 2003. So, if you have Office 2003 installed, one way to get around that problem is by installing the compatibility update available at this link.
From the website:
By installing the Compatibility Pack in addition to Microsoft Office 2000, Office XP, or Office 2003, you will be able to open, edit, and save files using the file formats new to Word, Excel, and PowerPoint 2007. The Compatibility Pack can also be used in conjunction with the Microsoft Office Word Viewer 2003, Excel Viewer 2003, and PowerPoint Viewer 2003 to view files saved in these new formats.