finding key pad code

According to justanswer.com, here's how.

There are two ways to obtain the code: one option is for the dealer to scan the system and retrieve it for you, or if the sticker is still present, you can find it in the vehicle security module located behind the rear seat back.

2006 Ford F150 Keyless Entry Code Location Guide

This page should give you enough information to remove your rear seat; I randomly picked a model but you can go back and select the specific model/drive/engine that you have if this isn't quite right.

Rear Seat — 2006 Ford F 150 2WD Pickup V8-4.6L VIN W Service Manual - Operation CHARM