It's not your documents that is the problem, it's the Office applications:
Office 2004 Applications Won't Work in Lion/Mountain Lion
You need to upgrade to Office 2011 - Mactopia - or you can try the freeware suite, Libre Office, that is functionally similar to Office 2007 for Windows except it works on Lion or Mountain Lion.
You may want to consider as well:
These two suites are similar to Libre Office but not as current or as well-supported:
NeoOffice
Open Office
And, then there is Apple's iWork suite:
Pages - word processing and layout
Keynote - presentation
Numbers - spreadsheet
Each can open and save Office compatible files. They may be purchased separately via the Mac App Store for $19.99 each.
(Access to the Mac App Store requires Snow Leopard 10.6.6 or higher and an Apple ID.)