Unfortunately, the data sheet that you linked to doesn't provide enough information. Specifically, where you apply the PWM signal, and what sort of drive it needs. I haven't been able to find this information on the web. unless the motor came wtih a manual, I think you will need to contact the manufacturer. My suspicion is that one of the thinner wires is a tacho output (the datasheet mentions this as an option), and one is the PWM input - both probably relative to the negative wire.
The P and O variants sound like different sorts of PWM input. The O variant sounds like a standard 0-10VDC analog control input, with a smoothing filter so that you can use a 10V PWM signal instead. I've come accross this arrangement before. The P variant could be a PWM input designed to be connected to an open-collector or open-drain current sink, like a PWM PC fan, given that the datasheet suggests that the fan will run at maximum speed if it is left open.