Abstract: A picture to be printed is prepared by DTP software and is stored into layer L0 of the file F which is distributed to respective correctors. The first corrector writes correcting indication K1 onto layer L1, the second corrector writes correcting indication K2 onto the layer L2 and the third corrector writes correcting indication K3 onto the layer L3. For the respective layers, respective passwords are to be set for ensuring securities. In order to display or to edit a specific layer, it is required to input a proper password. Layer information ranging over plural files can be united within a single file and are handled with a unified manner.