I think I found a solution
https://answers.microsoft.com/en-us/windows/forum/windows_10-files/windows-file-association-explained-for-desktop/cfa62c00-82e0-4d05-b302-3444ab930bb7
I understand windows xp and 7 ways but can someone help me win the new one?
and say if I can do this by code (I mean if I give someone my app, I want this to set automatically)