Several months ago, I received a question about opening up an excel file:
why can’t i open this attachment?
is it an excel file? my mac doesn’t recognize it?
The attached file had a .xlsx extension and that was the giveaway.
When Microsoft introduced Office 2007 (and 2008 for the Mac), they revamped the formats for all of the Microsoft Office file types. To differentiate the new file types, they added an ‘x’ to the format. So anything that ends in ‘x’ (.docx, pptx, xlsx, etc) were created by the new version of Office.
Microsoft has released a knowledge base article about it: How to use earlier versions of Excel, PowerPoint, and Word to open and save files from 2007 Office programs.
They have also released a compatibility fix, at least for Windows-based machines: Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats