PCSOFT use their WDZ format for most of anything and it's not standard so you wont be able to open it with the usual tools. I heard they used some of the usual libs like zlib but put their little twist to it so you probably could only work with their tool WDZIP.EXE to work with that.
You should look at other functions like zipCreate() for creating archives and using some standard formats: http://doc.windev.com/en-US/?3082007
Hope this helps :)