A program is neither a document, nor a folder. A program is actually a “tool” that you use to create, view, or print documents. Icons for programs do not have either the manila file folder symbol or the dog-eared piece of paper. Rather, the icon for a program is usually just the program’s logo. You can see this for yourself by clicking the Start button at the bottom left of the Windows computer display. As you can see down the left side of the sample Start menu below, there are no manila folders or dog-eared sheets of paper in the icons for these programs.
No document can open “by itself.” A document must open within a program. When you double-click on a document’s icon, the document opens using the default program for that document type. The logo superimposed over the “dog-eared sheet of paper” portion of a document’s icon corresponds to the logo of the default program for that document type. See below.
Documents, on the other hand, are things like typed text, pictures… the types of things you might actually store in a filing cabinet if they were on paper rather than on a computer. To keep this “paper” analogy, icons that represent documents tend to show a sheet of paper as part of their icon.