Do I need a visa or any other documents?

you will not be allowed entry into china this way, and they will most likely quarantine you and put you back on the first available flight, perhaps the same one that you intend to fly back with. anyhow, doubt you can meet anyhow during that 2 hour stay. however, if you get a ticket from Beijing to hong kong, then you can stay up to 72 hours in beijing , then fly to h.k and from h.k fly back to US