Adobe Acrobat Reader is the official, straight from the source, reader of the widely popular PDF files that are used by everyone from international businesses to students handing in assignments in university.
Adobe Reader is currently at version number 8, having covered a wide history of computer, starting with the Macintosh and Windows 3.1 platforms in 1993. Initially not a free program, a purchase made by the IRS essentially rendered the program free to the public. Acrobat Reader has gone through much over the years, to become more and more comprehensive and feature-laden. However, their latest version takes a step back to simplify the interface and help improve performance.
Starting with humble beginnings, Adobe (along with their Reader application) has grown leaps and bounds, including the purchase of Macromedia and their famous Flash technology.