Most compilers these days add the header files on their own. For example in HiTech if you just add either htc.h or pic.h it works. The IDE like Mplab chooses the device for you during compilation. This also makes it easier to switch between devices. If you want the header files look for "h" folder or an "include" folder in your compilers directory. in Hi- tech they are in : Program Files\HI-TECH Software\PICC\"<version>"\include