How do I find out the file type without an extension?

Ahh, the dark arts of file identification.

I rather like trid for this. It identifies files (and renames them, if you choose), has a nice large database, and is totally independent of the file itself, so you have two approaches at your disposal.

There is also FileID which uses magicdb

Explanation: FileID, TrID and File all work with magic numbers contained in the file which are supposed to be unique for each filetype, so all three programs are more or less equivalent. TrID is the most practical for windows users, while GNU/Linux ones simply use file.

You can try the file command for Windows