When a project team lacks hands-on experience and decides to involve a third-party vendor for product development, the first document to expedite is a Request for Proposal (RFP). An RFP outlines the project requirements and asks potential vendors to submit proposals detailing how they would meet those requirements and at what cost. This allows the project manager to evaluate the capabilities and offerings of different vendors before making a decision.
References = CompTIA Project+ Certification Study Guide (PK0-005)