Developed in 1982 by Adobe Systems, the .ps extension is a file type used by the publishing industry. Prior to the development of PostScript, it was not possible to print images and text on the same page. Postscript addressed this by defining a language that allowed applications to instruct the printer how to display objects on the page. This file type revolutionised publishing allowing certain curved items to be printed that previously could only be printed on specialist CAD printers. Although no longer as popular or common as it was historically, it is still an important file type.
PostScript is actually a programming language as well as a file type. Typically files are created by applications such as Adobe Acrobat or Quark Xpress. Now a legacy file format, most printers and programs continue to support this format, with the only pre-requisite being a printer utility that supports PostScript. The file basically contains a set of instructions that tell the printer what to print and provide the co-ordinates on the page of where an object or text should be printed.
PDF is a file format developed by Adobe Systems for representing documents in a manner that is separate from the original operating system, application or hardware from where it was originally created. A PDF file can be any length, contain any number of fonts and images and is designed to enable the creation and transfer of printer-ready output.
Each PDF file encapsulates a complete description of a 2D document (and, with the advent of Acrobat 3D, embedded 3D documents) that includes the text, fonts, images and 2D vector graphics that compose the document. They do not encode information that is specific to the application software, hardware, or operating system used to create or view the document.