Umm.. I'm pretty sure you have that backwards. You would want to process the .pcs with the executable... so something like
$ wine lz77ex.exe (filename).pcs
When people mention to drag the file onto the executable, that tries to parse the file using the executable in the windows world, so this will just need to be done by command prompt in Linux. I've never used this app myself, but hopefully it's just CLI and doesn't have some kind of built in GUI which could just screw things up for the way I mentioned.