I’ve read several times that PDF is “just compressed PostScript” but I recently learned that that’s not true. David Evans has a nice article over at Adobe on PostScript vs. PDF.
Evans starts off by describing what PostScript is and how it is used. Like most of my readers, none of that came as a surprise—I’ve even written some simple PostScript programs so I’m pretty familiar with it. The interesting part for me was his description of PDF and how it differs from PostScript. In addition to describing the words on a page, PDF contains other information such as fonts, images, hyperlinks, keywords, and so on. More important, however, is that the PDF file has already been processed by a Raster Image Processor and made into objects that can be viewed on screen. This has the added benefit that it gives a very clear indication of what the object will actually look like when it’s printed.
Evans writes that he believes more people will begin to deliver PDF files to printing services as better tools become available. That’s already happening. Between my first and second books, my publisher switched from asking for PostScript to asking for PDF to deliver to their printing vendor. I used to send all my memos, reports, and papers as PostScript and sometimes people (especially non-Unix people) would be unable to read them. Now, like everyone else, I send PDF and everyone can read them—even the printer.
Unless you’re already familiar with PostScript and PDF, this article is a useful introduction that’s worth a read.