To view and use the files, you need the free Acrobat Reader, which you can easily download. Once you've downloaded the Reader, it will start automatically whenever you want to look at a PDF file.

PDF files are especially useful for documents such as magazine articles, product brochures, or flyers in which you want to preserve the original graphic appearance online. A PDF file contains one or more page images, each of which you can zoom in on or out from. You can page forward and backward.

The Acrobat product that lets you create PDF files sells in the $200-300 range. A non-Adobe alternative is a product called Niknak from 5D, a company in the UK. (The Reader itself is free and can be used as a plug-in with your Web browser or can be started by itself.) Some situations in which PDF files are desirable include:

Graphic design development in which team members are working at a distance and need to explore design ideas online

Help desk people who need to see the printed book that users are looking at

The online distribution of any printed document in which you want to preserve its printed appearance

Acrobat's PDF files are more than images of documents. Files can embed type fonts so that they're available at any viewing location. They can also include interactive elements such as buttons for forms entry and for triggering sound and Quicktime or AVI movies. PDF files are optimized for the Web by rendering text before graphic images and hypertext links. Want to know more about PDF’s history, you can go to: http://freeipadapp.blog.fc2.com/blog-entry-4.html.