Acrobat PDF is perhaps the best format available to create printable documents, since it is optimized for letter sized sheets of paper.

Since Acrobat Reader can be opened within Internet Explorer, distributing PDF documents through the web has now become common practice. Acrobat is quickly becoming the format of choice to distribute instruction manuals, special reports, resumes, ebooks, etc.

However, all this comes at the price of increased usability problems when users try to read PDF documents directly from the screen; for example:

*The web page that links to the PDF file disappears after the PDF opens. Since PDF files don't have navigation bars some users may not know how to get back to where they were.

*Scrolling works differently: while scrolling HTML pages by dragging the scrollbar is linear, PDF files force users to scroll one full page at a time.

*Usually, PDF files come in small print (and Internet Explorer's Text Size options won't work on them).

*Since PDF documents are opened in Acrobat Reader, they introduce Acrobat's own toolbar, which contains menu buttons that are different from those in Internet Explorer.

These different "rules of engagement" are likely to cause user confusion. In order to make the user experience as painless as possible, you must consider three simple guidelines to effectively use PDF files on your site:

*Use them only to present printable versions of HTML documents (for example, a long article) or documents that are intended for print. Don't use them to present content to be read online.

*When linking to a PDF file, you must explicitly indicate that the destination page is in PDF format. This will tell your visitors what to expect, for example a longer waiting period than for an HTML document, or the fact that Acrobat Reader will open within their web browser.

*The best way to indicate that a link will point to a PDF file is either to use the Google convention of writing the symbols [PDF] before the link text, or to use a PDF icon.

*Clearly state the file size (to give users an idea of how long it will take to download) and the number of pages (so they can have the printer ready with enough sheets of paper). It is usually better to present these two pieces of information in a slightly more subdued font color than the one used for your page copy (if you're using black text copy, you can use gray).

Finally, even though most computers nowadays include Acrobat Reader as standard software, it is always good to include a link to the page where your visitors can download it, just in case they don't have it installed (the URL of the current download page for Acrobat Reader is: http://www.adobe.com/products/acrobat/main.html ).

About the author:
Mario Sanchez publishes The Internet Digest ( http://www.theinternetdigest.net ), an online collection of web design and Internet marketing articles and resources.  You can freely reprint his weekly articles in your website, ezine, newsletter or ebook.