If you wonder whether you can substitute one for the other, the answer is yes. You would use a lot less red chili powder, even if it is of the milder variety, than you would paprika. In fact, the best way to go about this is add it slowly and in small amounts, till you get the heat factor that you want. In a pinch, you can use paprika instead of red chili powder as well, though you may not get the color that you want and the flavor may be different.