Yip, really - lol.
I have been hacking away to create a temp fix.
Problem is that you can't associate .capx and caproj files with the steam version of C2. Because steam doesn't have a valid .exe file only a url and the exe file that is in the steam apps folder opens the free version download.
I have been hacking away with a fix - create a .bat file that opens an instance of C2, but can't get the file to load.
"%~dp0\steam.exe" -applaunch 227980 /fxsload=\"%1\"
save as c2.bat in steam.exe folder
Associate c2.bat with .capx and .caproj files.
But this only opens c2 not the file - my smarts are not strong with this one.
Oh, well, I'll have to do it the old way of open file via C2