Handling event when a new process(Application is opening)

If that can be done in C# then it would be WMI doing it; look at WMI. I think however that WMI does not do it. So you are left with undocumented solutions I think; undocumented by Microsoft that is. There are many articles and forum answers in other forums. I think the options include use of a Windows service (device driver type of service). You probably must inject code into the Windows low-level process creation; there are samples of that around that you can find if you look for it.
 
You can use a system-wide hook to hook top-level window creation and I assume you only need applications with a top-level window visible. I don't know if you can write a hook handler in C#; you might need to do a bit of C++ programming. You can certainly write the hook installer part (SetWindowsHookEx) using C#.