There are different situation when its not wise to do all project work , it might be skillet not available within organization or it might be more cost benefit to outsourced part of work. In either case PM need to perform Procurement Management. There might be a different team for procurement management with legal experts. But PM need to ensure to understand the contract terms and which vendor need to be awarded.
There are 4 processes in this knowledge area.
1 Plan Procurement Management
2 Conduct Procurements
3 Control Procurements
4 Close Procurement