Which of the following is a required document for a contractor before starting work?

A valid contractor's license is a critical requirement for a contractor to legally start work on a project. This license serves as proof that the contractor has met the necessary qualifications and standards set by the state or local regulatory authorities. It ensures that the contractor is legally recognized and permitted to undertake construction or specialty work, providing a level of protection for both the contractor and the clients they serve.

While project blueprints, supplier contracts, and employee manuals may be important for the execution and management of a project, they are not legally required documents for the contractor to commence work. The contractor's license is a fundamental requirement that confirms competency and compliance with regulatory standards, making it essential for starting any contracting work.