Where are programs saving license?

Hello, i've lost key code of very important program for me... I have it on my harddisk but he is near end of his life so i need to reinstall it to other pc but i lost CD-Key so i can't install it.. Is there some way to get the key or bypass instalation?

Contact the publishers support. Maybe they can help you.

Maybe in the Windows registry?

About which program we are talking?
That we can help you, we need to know which program do you mean :D