Ninthchamber asked the Office & Business Software forum why OpenOffice files don't always open in Microsoft Office.
The free OpenOffice suite is relatively compatible with Microsoft Office, but not perfectly. It's best to understand what will work with what.
For simplicity's sake, I'm sticking to word processing files here. But the basic rules apply to other office formats, as well.
When you save a document, OpenOffice defaults to its own .odf file format. Microsoft added support for .odf files with Office 2007 SP2. If someone with whom you're sharing files has a pre-2007 version of Office, or a copy of Office 2007 in bad need of an update, they will not be able to load your file.