If that is a platinum RTD, you will need to send a currrent through it from a controlles source. Using a high-quality amplifier, amplify the voltage on the RTD up to a level compatible with the A to D converter in the PIC. After conversion, apply the values against a look-up table to linearize the signal.
One observation, though - an RTD is a very expensive and precise measurement device. Reading it with an 8 or 10 bit A to D is a bit like measuring dimensions in ells and spans. The units are just too coarse to give good results.