Do you know, any document that explain about ADC for dummies?

I would go to the websites of 'Analog Devices', 'Texas Instruments', 'Maxim', 'Linear Technology', etc. They have many applications notes about this issue.

But the easiest way to learn about ADCs is just to have a look at those several datasheets available. In former times, when internet wasn't borne, we had big databooks. And reading them was like reading in a textbook! Often, certain datasheets are incomplete in some points. Others, on the other hand, go into total detail. So, it's best to read as many as possible datasheets about ADCs, even if they might be totally different in their specifications. After some time you get an idea of what is going on...

Good luck,
Kai