It is 20 years since Adobe first began talking about its idea for a portable document format (PDF) that would allow printed material to appear the same on screen as on paper.
The PDF meant that for the first time it was possible to create a digital image in a standard format that could be distributed to computers running any operating system.
It was a breakthrough: brochures, magazines, newspapers, and all manner of commercial documents could be passed around electronically.
“PDFs are so easy to create that millions of them are produced each day either by exporting them from applications or by scanning paper documents,” explains James Townsend, web developer at Shaw Trust.
However, most are inaccessible because their creators have not taken the trouble to make use of the tools that are available.
“Originally PDFs were geared to the print industry,” says Townsend. “Even today, the main use of PDFs is for scanning documents, which means one can see the documents but can’t interact with them.
“They are a bitmap image, so people who use a screen reader, for example, can’t access them.
“To make a PDF image file accessible, the document needs to be captured using Adobe Acrobat Capture 3 or the paper capture facility provided with Acrobat 6.”
It wasn’t until 2001 that Adobe began to make PDFs accessible, largely because of the introduction of section 508, US regulations requiring public sector systems usable by disabled citizens.
Acrobat 5, Adobe’s program for making and editing PDFs, introduced the concept of tagging.
Tags indicate the structure of a document, telling assistive software the order to read it in and flagging the presence of figures, lists, tables and so on. Initially a manual exercise, tagging is now automated.
The ability to read out screens came in with Acrobat 6, while the latest iteration of Acrobat – Acrobat X – has a wizard to check if a document is accessible or not.
Tagged PDF files work better with the screen-reader devices used by many blind and other disabled users.
But unless a document is very simple indeed, automated tagging alone will not give the best result. Human intervention is needed to make sure the tagging is good enough to make sense of a document.
“But it is not necessarily complex or time consuming,” says Townsend. “Tagging takes a few seconds, but as with a website you need to start thinking about accessibility right at the beginning.”
He stresses that authors should make sure that the reading order of their content is clear, logical and easy to follow.
The TouchUp Reading Order tool allows a user to quickly add and edit PDF tags and view the reading order of elements on the page. Although it can speed up the tagging process, it does not take the place of the other tools.
“It is important to make sure that all images that convey useful information, such as a photograph or a diagram, rather than just being decorative, have text alternatives, or ‘alt text’,” says Townsend.
Purely decorative images or repeated headers and footers should be removed from the reading order so that users of screen readers and other assistive technology are not troubled by repetitive or unnecessary announcements.
“An accessible PDF must include correctly formatted structural elements such as headings, a table of contents, links and bookmarks,” explains Townsend. “Text should be formatted in such a way that it will be readable by people with vision impairments or cognitive disabilities such as dyslexia.”
“It is important to specify which human language the document is written in, to allow assistive software to work properly,” Townsend points out.
“The document’s security settings (if any) must not exclude users of assistive technologies. It is possible to lock a document to protect copyright material. However, this can prevent some disabled people gaining access to it.”
Making PDFs accessible is not very difficult, if you follow these simple steps, but it can make a big difference to the millions of people around the world who use assistive technology.
Web Access is sponsored by Shaw Trust