Mikro C pwM1_Set_Duty definition
What you're asking in this question not possible in MikroC. It is Mikroelektronika's policy not to provide source code for library functions. Such is life when you're using closed-source tools.

The closest you can go is to start a project, compile it, look at the assembly code of the function and try to do something with it.

As for the comment, well I managed to build the PWM example with PIC18f452 selected and t built fine, but I don't have one available to test if it's actually working.