You must modify and recompile your source code. It doesn't work on already-compiled files. Also, the free version adds a nag screen? (Historically, no nag for SDK use, but check current EULA).
has long been a trusted commercial solution to this problem. It offers a robust suite: registry protection, anti-debugging, file packing, and a licensing server. However, with commercial licenses starting at several hundred dollars, indie developers and hobbyists often look for an "enigma protector alternative free." enigma protector alternative free
Requires web development skills. You must implement anti-debugging yourself (though you can combine it with ConfuserEx). You must modify and recompile your source code