Andy, document says about "specified" files but dont specify anything not even where to find it, I have searched for it also gave a look in wellgain website and found nothing. Maybe I'm doing wrong (I'm not a professional).

lmgtfy is a bit offensive as I have searched and searched lots, my error was to search for "micro stepping" instead of "microstepping"

I already know http://www.divms.uiowa.edu/~jones/step/micro.html website, it gives me headche because I cant understand almost all.

Seen all that and with a new search using the right key word I just found microstepping + pwm is possible, but I still in doubt on how to code this...
I know how to control a commom unipolar stepper motor (full and half step) and know how to code a pwm, but I'm very doubt about how to do in this one which is bipolar.
There are 4 pins, 2 coils, only 2 pins will be active at same time, the other two will be 0v so I can invert the polarity, how the best way to do this?
4 pwm channels (1 for each pin) or some other kind of pwm coding?

Thank you.