I can't answer this off hand, but if you look at how the search page is implemented in the MVC templates, along with the classes that it uses for searching, you should be able to figure this out. Amongst other things, the templates contain code for checking if a response item is a file.
I am trying to implement a search page and I was able to get a list of "IndexResponseItem".
The problem is that beside the pages I am also getting images, documents etc. and I would like to be able to exclude some folders and select some folder for the search but I have no idea how to do it? Any idea?