PDF files are only good for one thing; distributing documents that need to be printed. It can be so tempting when faced with a lot of printed content that needs to be displayed on the web to simply create a series of PDF documents and upload them. However PDF files should never be used when you expect users to read the content online.
The problem with PDF
PDF was designed for printing. It was never intended to be viewed on screen. The result is that it causes serious usability problems. Jacob Nielsen estimates that PDF files make usability approximately 300% worse compared with an HTML page.
So what exactly is the problem:
It is a print orientated viewer
PDF was never designed for on screen viewing. Rather it was design for print which means the size of most pages is A4 or letter rather than any standard screen resolution like 800 by 600. This means that the user only sees a small portion of the document they are viewing and cannot scroll through it in the linear manner you would a HTML page. The document is split up into pages which are more orientated around the design and layout instead of the content as you would find on a web page.
Because PDF was not originally designed for a web environment they are often graphically heavy and tend to be considerably bigger than the standard HTML page. In addition to this the PDF is downloaded as a single document irrespective of how many pages it contains. This can lead to frustratingly long download time for a whole document when you might only require a single page.
Lack of hypertext linking
Although it is possible to add hypertext links into a PDF document it rarely happens. The ability to quickly skip around the document in order to find the content you require is therefore absent and the user is left with substantial amounts of scrolling.
While not generally a common problem tests have shown that you are more likely to cause a users PC to crash with a PDF than a normal HTML web page. Apparently this a particular problem on older Mac computers.
Non standard interface
One of the biggest problems with PDF documents in my opinion is that they do not have a standard web interface. For example scrolling works in a different way to a conventional web site. Also, after finishing with a PDF document, users sometimes close the window instead of clicking the Back button, thus losing the web site they were viewing.
The need for a reader
Of course the number one problem with a PDF document is that it requires a special reader to view it. Even the most basic version of the Acrobat reader currently standards at 8.7mb! This is a substantial download especially on a dial up connection. Although many PC’s already have acrobat reader it may still be necessary to download the newest version of the plug in because the PDF file being viewed is a more recent version.
Guidelines for using PDF
So is there ever a time when PDF is a good idea? Yes of course there is. Like so many things in life it is important to use the right tool for the right job. PDF was designed for print and so that is when it should be used. Because people don’t like to read large amount of content on screen a PDF file might be the solution when the user is required to read 5 pages or more. Equally a PDF is a good candidate if you want to provide the user with a printable summary of an entire site.
When you do choose to have a PDF document I would recommend you follow these simple guidelines:
Create an HTML gateway page
Instead of linking directly to a PDF file, link to an HTML gateway page instead. On this page provide:
- a summary of what the document contains,
- the file size of the PDF file (including estimated download time),
- a link to the Adobe site where they can download the Acrobat reader.
State clearly PDF is for print
State clearly that the PDF file is for printing only. Present the same content on the web site in traditional formats, and provide links to them for readers who prefer to read online or don’t wish to install Acrobat Reader. This is important from an accessibility perspective.
Never let a search engine index your PDF
The problem with allowing search engines to spider your PDF documents is that it will then link to them directly. This means the user is dumped into the PDF without any clear idea of what it is about or how long it will take to download. Also they get no sense of context of the document within the rest of your site. Let the search engines index your gateway pages instead.
Avoid the latest version of the PDF format
As I have already mentioned above, building PDF files in the latest format may force many users to download the latest plug in if they wish to view the content. You simply cannot guarantee everybody will have the latest version of Acrobat. As a general rule of thumb I would recommend that you ensure your PDF documents are at least one version behind the latest format.
Remember that not every country uses the same standard paper sizes. Some countries use 8.5×11, while others use A4. Make sure your document will fit both.