Steam achievement question

Just wanted to ask if anybody knows if game achievements for Steam triggers only after you bought the game, or if it triggers for the demo too? Looking at what Steam says, it depends a bit on how the demo is uploaded in the first place.

The reason I ask, is because I want to try to see if I can use the achievements to see what percentage of people actually continues playing past the demo.

Steam demos have different app id compared to full game. So achievements don’t count from them.