You create an article by defining a series
of boxes around the content in the order in which you want the content
read. The navigational path you define for an article is known as
the
article thread. You create a thread connecting
the various boxes, unifying them into a continuous text flow.

Most desktop publishing programs allow you to generate
article threads automatically as you convert the files to Adobe
PDF. If the file you’re viewing has articles, you can show the names
of the articles on a tab and navigate easily through them.