PIC18F14K50 with 8Mhz crystal and 50Hz PWM
If you really need to operate that slowly (usually faster is better, at least up to some kHz for PWM) then you have a couple choices- use a slower clock frequency (much lower, so maybe not desirable- but slower clock means less power consumption). It also does not give you fine resolution on the PWM period (because normally nobody cares that much as long as it is fast enough).  

Or you can use the timer compare function to provide sub-microsecond accurate transitions since it can toggle the pin with the hardware compare function- you then set it up for the next compare (and, optionally, toggle the output pin). That would be the preferred approach, in my opinion. 

Some of the 16F series parts have a numerically controlled oscillator peripheral (NCO), but I don't think it's available in the 18F series (could be wrong).