A document printing system may include a print engine, a controller coupled to the print engine and a communication port in electrical communication with the controller. The communication port can read a portable memory device, which stores an electronic secure file for authorizing the print engine. The portable memory device may store data such as the device identification code, the vendor identification code, the creation date for the electronic secure file. The electronic secure file may also store the device identification code, the vendor identification code, the creation date for the file itself, as well as a balance amount. The system may authorize a print engine by comparing the data in the electronic secure file and data stored on the portable memory device. If the comparison of data finds a mismatch, the system may determine that the print engine is not authorized; or that the service is authorized if otherwise.