A word processing file contains user information in plain text or rich text format. A plain text file format contains unformatted text and no font or page settings etc. can be applied. In contrast, a rich text file format allows formatting options such as setting fonts type, styles (bold, italic, underline, etc.), page margins, headings, bullets and numbers, and several other formatting features.
Portable Document Format (PDF) is a type of document created by Adobe back in 1990s. The purpose of this file format was to introduce a standard for representation of documents and other reference material in a format that is independent of application software, hardware as well as Operating System. PDF files can be opened in Adobe Acrobat Reader/Writer as well in most modern browsers like Chrome, Safari, Firefox via extensions/plug-ins.
You can also convert WORD into many other file formats. Please see the complete list below.