A method for enforcing a contract for a computer-aided-design (CAD) tool is provided. In this method, a first payment for the CAD tool is made in accordance with the contract. The first payment is associated with user access to the CAD tool. At this point, the CAD tool can be used, wherein the computer system running the CAD tool includes criteria for requesting at least one additional payment for the CAD tool. Each additional payment is associated with generating an output. The computer system is responsive to one or more trigger conditions corresponding to the criteria. A payment request is received when an output generated by the CAD tool satisfies a trigger condition. For example, one trigger condition adds a watermark to the output for identifying the output as having been produced by the CAD tool.