Is there an app for opening window files?

what do you mean window files. if you mean browsing through files, OS X can look through them.

specify the extension of the file, if that's what you're talking about.

 

By window files, do you mean Windows files? And can you be more specific about what these files are? It’s impossible to answer the question without knowing more. If you’re talking about something like images or documents, you should have no problem. But if you’re talking about programs, then that’s a different story. You would need Windows to run those (although Crossover has some products for running Windows software, but I don’t know much about those). VMWare can run Windows inside of OS X, but you would still need an actual copy of Windows to do so. If you run Windows inside VMWare, you can, of course, run Windows programs inside Windows.

 

i think it's obvious that the OP is asking about running windows programs, not opening files.

 

I don’t think that’s obvious, I’ve seen people asking that didn’t know if you could open Word documents or pictures from PCs on a Mac.

You say program or file. Again, it makes a big difference exactly what you’re trying to open. If it’s just something like music or a document, you won’t need anything like Crossover.

 

A Beginner's Guide to Running Windows on a Mac
http://guides.macrumors.com/A_Beginner's_Guide_to_Running_Windows_on_a_Mac