Ever wondered why you can't open Microsoft Office 2007 files in Microsoft Office 2003 or previous versions? For example, a Word 2007 file in .docx format cannot be opened in Word 2003 which reads files in .doc format. Well, it's simply because of a compatibility issue.
Now you don't have to upgrade just to solve that. There is already a solution - the Microsoft Office "Compatibility Pack" called FileFormatConverters.
According to Microsoft, "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.
Download Microsoft Office Compatibility Pack