l buy a 2004 lincon aviator but loose my door code the manual book say to enter the factory code and add my new codebut dontknow the factory code

every one is different for each vehicle.

Open the right/rear door. Gently pull the on-body weatherstrip slightly away from the body at the rear side of the door opening. Fold & lock the right/rear seat back down into the locked position. Carefully pull the trim panel that houses the seat belt height adjuster & anchor pivot off of the body. Now carefully pull the lower trim panel from the inside outward far enough to expose the VSM (Vehicle Security Module). This module has three electrical connectors plugged into it, coloured green, grey & blue. On the module is a label bearing a number similar to 4L2T-15K602-EA. On the same label will be FIVE large numbers. Those five numbers r ur five digit keyless entry keypad code. Hope this helps.

My advice would be to take it to your Lincoln dealer and have them reset it. It will cost you $25-35.