Adobe Reader
Adobe Reader is formerly known as Acrobat Reader. The name change comes from some confusion between another product called Acrobat and the reader for the Acrobat files.
Acrobat Reader is required to view files with the PDF (Portable Document Files) extension. This format is popular because it is universal in the way it displays images and text. Presentations and instruction manuals are usually written in this format. You will need to get Acrobat Reader sooner or later. It is free and non-obtrusive.