A method for updating an ISO file, e.g., to add a digital signature to the ISO file, includes adding a supplemental file composed of, e.g., all zeroes to the ISO file before recording, and then recording the ISO file with supplemental file to an optical disk using ISO format. A digital signature is computed after recording. The zeroes in the supplemental file are replaced by the values of the digital signature and the file is re-saved. Also, an ISO file that might have a common part and several unique parts, e.g., for respective languages, is deconstructed such that only a single copy of the common part is recorded to disk, avoiding multiple recordations of the same data.