A response to 'Avoid PDF for On-Screen Reading' column
Adobe ePaper staffer rebuts Jakob Nielsen's recent Alertbox column

Editor's Note: The following letter to Jakob Nielsen, written in response to a recent useability column that discounted many of the features of Adobe Acrobat and PDF, is being re-published with the expressed permission of the author, Robert McDaniels of Adobe Systems Incorporated. McDaniels also posted his response in the PDF-Talkback section of the Planet PDF Forum, and on several other lists.

12 June 2001

Hi Dr. Nielsen,

In your June 10, 2001 Alertbox column titled "Avoid PDF for On-Screen Reading," you made some comments about the consequences of using PDFs in an HTML world, but most of the information you posted was not accurate and perpetuated many PDF myths that we at Adobe have spent years clarifying.

While PDF is not the native format for a browser, it is supported on more than 200 million computers that have downloaded the Acrobat Reader. You mention PDF as a way of transferring material meant for print, and this is a task that PDF is excellent for, but it is only the tip of the iceberg when it comes to PDF's Web capabilities.

It looks like what you are really criticizing is bad PDF design, not the PDF format, because PDF actually does all of the things you claim it cannot. Just as there are terrible HTML pages there are also terrible PDF pages, but this is a fault of the designer not the file format. I think this is an important distinction that you did not make. Some corrections on PDF uses to contrast what was in your article are listed below:

>> "PDF is great for distributing documents that need to be printed. But that is all it's good for."

The Adobe Acrobat Reader supports hyperlinking, rollovers, bookmarks, thumbnail views, audio and video content, fillable form fields, document searching (with thesaurus, word stemming, proximity, case matching, and "sounds like" options), article threads, document reflow for display on narrow windows or even Palm OS devices (yes, the Palm OS Reader is available - no such animal for HTML), embedding vector information, document security, JavaScript, XML tagging, ODBC integration, font embedding, and many features that HTML is not capable of.

Many of the supported features in PDF are also much better than what HTML can do. For example, a PDF form is not constrained to the standard HTML form appearance. So if little, beveled gray boxes do not fit with the rest of your web site's look and feel, too bad if you use HTML forms. Also, PDF forms can be submitted in many formats (FDF - the PDF form info, HTML, XML, or the entire PDF file).

Using the full version of Adobe Acrobat, you get many even more powerful features like:

  • Digital signatures (now legally binding)
  • Online comment posting and review
  • Capturing HTML pages (links and images intact) for offline viewing or distribution

and much more.

>> "Forcing users to browse PDF documents can reduce your website's usability by about 300% relative to HTML pages."

By turning off what Adobe Acrobat menu items are visible when a PDF is opened (an option that the PDF author can set), I can create a PDF that opens in a Web browser without the Acrobat Reader menu visible, and 90% of the viewers won't know it's not an HTML page. In addition, the 10% that do know it's a PDF are Web-savvy enough not to be confused by PDF's anyway.

>> "PDF was designed to specify printable pages. PDF content is thus optimized for letter-sized sheets of paper, not for display in a browser window."

Actually, the PDF author can decide on any page size they want (just like an HTML author), and they can determine how the page is displayed (full screen, make the page width fit, make entire page fit, or any other view they choose). Not all of these options are available in HTML.

>> "PDF pages lack navigation bars and other apparatus that might help users move within the information space."

A PDF author can put all the navigation they want on a PDF page. The same statement can be said for HTML documents whose authors don't add navigational features. PDF's navigational features include many things not available in HTML.

PDF documents can have:

  • Hierarchal bookmarks
  • Thumbnails
  • Article threads
  • Links within a document
  • Links to views within a document
  • Links to other documents
  • Links to the web
  • Forward and back buttons
  • Buttons that execute menu commands like "File->Print"

One great feature for PDFs that you do want to print is that you can define your navigation buttons as "visible but not printable" so your online navigation does not clutter your print output. Try that with HTML :-)

>> "Because PDF documents can be very big, the inability to easily navigate them takes a toll on users. PDF documents also typically lack hypertext, again because they are designed with print in mind."

Again, it is up to the document author to include these features and not a limitation of the PDF format.

You also refer to PDF files as large. This again depends on the document author. Acrobat Distiller (the application that creates PDFs from PostScript) allows you to compress images to reduce your file size. You can also optimize files for display on the web to identify repeated graphics and support byte-serving (page-at-a-time downloading).

>> "In a recent study of how journalists use the Web, we found that PDF files sometimes crashed the user's computer."

Was the PDF file found to be the culprit and all other possibilities eliminated (user settings, OS problems, browser errors, etc.)? If so, please send the files, a description of the errors, and the information about the computers to me and I will submit a bug report to help ensure that any problems will be addressed. The same can be said for HTML pages w/ DHTML, CSS2, SWF content and a host of other features not available on older machines w/ old software.

>> "Because PDF is not the standard Web page format, it dumps users into a non-standard user interface."

Again, I can create a PDF that opens in a Web browser without the Acrobat Reader menu visible, and 90% of the viewers won't know it's not an HTML page.

>> "Also, after finishing with a PDF document, users sometimes close the window instead of clicking the Back button, thus losing their navigation history."

Most HTML designers open PDFs in a separate browser window if they are worried about this. It is a common technique.

Re: 'Guidelines for Using PDF:'

>> "You should use PDF only for documents that users need to download and print."

Forms, slide shows, documents that need security settings, documents that need to be searched (PDF search tools are better than HTML's), documents that need sound (sound files are embedded in the PDF and always play reliably, HTML pages with sound rely on the sound plug-in to be JavaScript-controllable, which works sometimes), files that require color management, and many more uses.

>> "As with any Internet software, many users are slow to upgrade when new formats ship. PDF version 5 was released recently, but I recommend sticking to version 3 until 2002."

The current PDF version is 1.4 (it does not parallel the Acrobat Reader version number). FYI; Acrobat Reader 3 -> PDF 1.2, Acrobat Reader 4 -> PDF 1.3, Acrobat Reader 5 -> PDF 1.4

>> "Format your printable documents for different sizes of paper. Some countries use 8.5x11, while others use A4. Make sure your document will fit both."

Using Acrobat, it is easy enough to create both formats from a single source file and allow the user to choose the format.

Two other important points to address:

  1. Adobe is constantly working to make the PDF format more accessible to the sight-impaired. More information on creating accessible PDFs is available on Adobe's Web site in our ePaper section.

  2. PDF files can easily be created from any application that prints. HTML must be authored in an HTML application or hand-coded in a text editor.

I am not saying that the PDF format is the best option in all cases, but to say that PDFs on the Web are big, don't display well, and are only good for printing is wrong. Maybe an Alertbox article that highlights how PDFs can be used on the Web would be more appropriate than one that misinforms the reader about the PDF format.

Sorry for the long reply (if you made it this far), but we at Adobe are dedicated to the PDF format, and your article simply discounted more than 90% of its great features.

Robert McDaniels
Application Engineer, Web & ePaper
Adobe Systems Incorporated


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