13. A computer program product comprising a computer usable non-transitory medium having a computer readable code embodied therein for controlling a printing device, wherein the printing device includes an input tray for holding printing sheets and an insert sheet tray for holding insert sheets, the computer readable program code configured to cause the printing device to execute a process for producing a print job, the process comprising the steps of: (a) receiving data representing a document to be printed in the print job; (b) receiving job information about the print job, the job information including an instruction to print multiple copies of the document; (c) printing the requested multiple copies of the document using the printing sheets from the input tray; (d) determining whether insert sheets are available in the insert sheet tray; (e) if insert sheets are available in the insert sheet tray, inserting insert sheets from the insert sheet tray between printed copies of the document; and (f) if insert sheets are unavailable in the insert sheet tray, printing one or more simulated insert sheets using the printing sheets from the input tray as a substitute and inserting them between printed copies of the document.
16. The computer program product of claim 13 , wherein the job information includes a parameter indicating whether simulated insert sheets are to be printed, and wherein in step (f) the simulated insert sheets are printed if the parameter indicates that simulated insert sheets are to be printed.