How do I use Umodel to port from Postal 2?

I want to port from Postal 2 and the easiest way I can find is umodel but it never works. I open it and then it closes right away. My friend told me to drop the files onto it but that didn’t work, I tried to put the exe file on it and got nothing, I also tried to put it in the folders and nothing. Is 3DX Ripper the only way to port from Postal?

There are some programs that can “open” *.UKX files, and allows to extract *.PSK. The UModel works sometimes. I can’t remember the other names.