Mac OS X

Mac OS X was a series of graphical operating systems developed and marketed by Apple for its Macintosh line of computers. It succeeded the "classic" Mac OS (which dates back to the launch of the original Macintosh in 1984) and NeXTSTEP (which was developed at NeXT after Steve Jobs left Apple). It has since been superseded by macOS, starting with macOS 10.12 "Sierra".

Native PDF support
Mac OS X used a PDF-based imaging model called Quartz. This replaced NeXTSTEP's Display PostScript implementation to avoid royalty fees to Adobe Systems. However, as Mac OS X's use of PDF prioritizes speed and compatibility over features and compression, it is limited to PDF 1.3 (or PDF 1.4 for document "bundles" which contain embedded graphics). Newer PDF files will either display incorrectly or cause a performance hit as Mac OS X will internally downconvert the document for display.