From Adobe Systems:
Create Adobe PDF enables you to easily create a PDF file from any application using the AdobePS 8.6 PostScript printer driver. It makes creating PDF files as easy as printing to a printer.
If you own Adobe Acrobat 4.0 for Mac OS and you use AdobePS 8.6 (the Adobe PostScript Printer driver) to print to PostScript devices, Adobe recommends that you install Create Adobe PDF. AdobePS 8.6 is available for free download from the Adobe Web site.
After you install Create Adobe PDF, you can select a special printer called "Create Adobe PDF" from within the Page Setup or Print dialog of AdobePS 8.6.