How to set page size for Postscript output file in Adobe InDesign CS5?
Change the PPD file! When you print to a PostScript printer, PostScript file, or PDF, Indesign automatically uses the default PPD (PostScript Printer Description) for that device. You must switch to a different one to suit your needs.
Choose File > Print. From the PPD menu, select one of the following: A PPD that corresponds to the current output device.
Other. Lets you select a custom PPD, such as one provided by your service bureau for use with the specified printer. The PPDâ€™s filename corresponds to the printerâ€™s or imagesetterâ€™s name and model, and may display a .ppd file extension (depending on how your system is set up.) Navigate to the PPD you want, select it, and click Open.
Note: Certain PPD features commonly found in imagesetter PPDs arenâ€™t accessible from the Indesign Print dialog box. To set those printer-specific features, click Setup (Windows) or Printer (Mac OS) in the Print dialog box.