MSG is a file format used by Microsoft Outlook and Exchange to store email messages, contact, appointment, or other tasks. Such messages may contain one or more email fields, with the sender, recipient, subject, date, and message body, or contact information, appointment particulars, and one or more task specifications. The properties that constitute the Message object, including are also a part of the MSG file.
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 MSG into many other file formats. Please see the complete list below.