how to use Proximity Inductive Sensor in Pic18F4550

there is tons of them. i normally use SFH6206-3T (SMT) or SFH620A-3 (through hole). they have high CTR and AC input so my projects get isolation and can work with either polarity. thanks to high CTR, i get decent coverage for input voltages so i don't have to switch resistors for different signal sources.
in your case this is not important because you know that source is 12V so you can go with just about anything incl. lower CTR (proxy will easily match current needs for your opto).

So i can use it for dc/dc circuits eventhough it has an AC input? Reason for asking is that the Proximity switch i'm going to use is a 6 to 36 volt DC switch..

correct....

AC input means it is 'universal' because there are two LEDs in it so polarity on input does not matter.