Hk to Beijing and then to Pakistan

If Beijing is your only stop in mainland China and if your entire layover there is shorter than 24 hours, you will be covered by 24 hour visa free transit and you do not need any kind of visa. In other words, if your flight itinerary is exactly as I have written, you are good to go. If you travel on a single ticket, you will just proceed from the exit from your plane toward the gate for your flight to Pakistan and during this segment you will not even be inspected by Chinese immigration, but you will just cross the security check. That's all.