PDF is a proprietary electronic document format developed by Adobe Inc. Initially, PDF was made for US federal authorities to store working documents, and now this format is de-facto standard of electronic document circulation. PDF documents are used in different fields: in industry, in services, in educational institutions, for personal exchange of information and so on (see Why use PDF section for more examples).
PDF documents can be opened on any popular platform – Linux, Windows, Mac (see PDF Pluses and Minuses section), and they always look identical, because the file itself stores fonts, palettes and media content used in the document. Besides, hot links and interactive content are also available, and a file can be protected with a password.