The primary function of a choke valve is for flow restriction. Choke valves are highly susceptible to erosion / flow damage by the nature of their operation, particularly where solid particles are present in the process medium.
Choke valves are not designed to reduce pressure.
The operation of a choke valve is generally by a hand wheel device screwing down a stem, which is connected to a “flow limiter” device (for example a cylinder with a hole in it).
As the cylinder rises and falls in the sleeved bore, the cross sectional area for flow increases or decreases accordingly. Choke valve occasionally have “full closure” capability.