The Free On-line Dictionary of Computing (30 December 2018):

Portable Document Format
PDF

    (PDF) The native file format for Adobe
   Systems' Acrobat.  PDF is the file format for representing
   documents in a manner that is independent of the original
   application software, hardware, and operating system used to
   create those documents.  A PDF file can describe documents
   containing any combination of text, graphics, and images in a
   device-independent and resolution independent format.  These
   documents can be one page or thousands of pages, very simple
   or extremely complex with a rich use of fonts, graphics,
   colour, and images.

   (http://adobe.com/products/acrobat/adobepdf.html).

   ["The Portable Document Format Reference Manual", Adobe
   systems, Inc. Addison-Wesley Publ.  Co., ISBN: 0-201-62628-4].

   (2000-09-08)