Depending on the prepress software available, a service provider may be able to perform such prepress activities as trapping, imposition, separating, and OPI replacement at the output device’s RIP. Therefore, your service provider may prefer to receive a composite PostScript file of the document optimized for in-RIP separations rather than a preseparated PostScript file.
Saving the file as PostScript preserves the separation settings, the PPD information, and any color conversions you have specified in the Advanced Print Setup dialog box.
For best results when generating PostScript for reuse in a print production workflow, use the Save As command rather than the Print To File option available in the Print dialog box.