but on the 18F4620 the port is digital as per the datasheet. If you want to use for ADC, then you must specify it on code.
That is the part you have backwards. You have to make the pins digital.

So... refer to the link I gave you and try
Code:
ADCON1=15
Keep reading chapter 19 and look at
REGISTER 19-2: ADCON1: A/D CONTROL REGISTER 1