Some strong opinions from Jakob Nielsen about PDFs...
Jakob Nielsen's Alertbox, June 10, 2001: Avoid PDF for On-Screen Reading Forcing users to browse PDF files makes usability approximately 300% worse compared to HTML pages. Only use PDF for documents that users are likely to print. In those cases, following six basic guidelines will minimize usability problems. * Create a gateway HTML page that summarizes the PDF file. * State clearly that the PDF file is for printing only and present the same content on other Web pages in traditional formats. * Link only to the gateway page. * Never let your search engines index the PDF file * Ensure that your PDF document format is at least one version behind the latest offering. * Format your printable documents for different sizes of paper. Jakob Nielsen's Alertbox, July 14, 2003: PDF: Unfit for Human Consumption Users get lost inside PDF files, which are typically big, linear text blobs that are optimized for print and unpleasant to read and navigate online. PDF is good for printing, but that's it. Don't use it for online presentation. PDF Usability Crimes * Linear exposition. * Jarring user experience. * Crashes and software problems. * Breaks flow. * Orphaned location. * Content blob. * Text fits the printed page, not a computer screen.