This is also in that PDF
The two GND, ACM and DCM ground terminals are isolated from each other. This keeps the optoisolators separated from the computer USB ground. The two GND terminals do connect to the computer USB ground. The +5V terminal is the same as computer USB +5 and caution should be taken if you use this terminal to power external devices. There is a 3.3 volt on board regulator for the STM32 microcontroller use only. There is no 3.3 volt screw terminal connector.