PDF

The Portable Document Format (PDF) is a file format standard that was originally created by Adobe to represent two-dimensional (and later three-dimensional) documents in a device and display resolution-independent fixed layout format. It is based from PostScript, an earlier Adobe product that was more focused on printer imaging.

PDF in Mac OS X
The PDF format, prior to becoming an ISO-certified standard, began as a proprietary technology of Adobe Systems to monetize their technology, as had been done with PostScript.

In the days of NeXTSTEP, NeXT Computer payed Adobe royalties in order to use Adobe's implementation of PostScript in NeXTSTEP's next-generation window system, Display PostScript. However, when NeXTSTEP was bought by Apple and eventually rewritten as Mac OS X, the decision was made to drop Display PostScript and to reverse-engineer Adobe's implementation of PDF (which had many features and advantages over PostScript in text and graphics rendering) in order to avoid paying Adobe royalties.

The result of this was Quartz, namely Quartz 2D, which draws OS X's 2D graphics using Apple's implementation of PDF. This also resulted in Preview, which also opens and renders PDFs natively.