After selecting file in "open dialog" or after other actions that make uniview to open some file, a complicated process overruns. It finds file type using it's contents (thus not just using extension). This makes UniView to open files correctly, even if they have wrong extension. If file does have other extension than it should have and if you checked possibility "ask user if file has improper extension", you will be noticed about it and you can correct extension straight. It's recommended to check 2nd checkbox too. This will delay file reading in some VERY RARE cases, but you will reach more successful file recognizing and reading...