When considering the accessibility of a document, it must meet certain technical criteria and must be able to be used by people with disabilities. This includes access by people who are mobility impaired, blind, low vision, deaf, hard of hearing, or who have cognitive impairments. By utilizing the technologies available through screen readers, text-to-speech, refreshable Braille displays, and other assistive technology, we can provide information to people with disabilities in formats that were once unavailable.
The Web Content Accessibility Guidelines (WCAG) 2.0 (ISO/IEC 40500:2012) and the PDF/UA (ISO 14289-1) standard cover a wide range of recommendations for making content more accessible to people with disabilities. One benefit of following these guidelines is that the content becomes more available for all users. For example, the underlying structure of a document makes it possible for a screen reader to properly read a PDF aloud and also makes it possible for mobile devices to correctly reflow and display the document on a smaller screen. By the same token, the preset tab order of an accessible PDF form helps all users – not just those who rely on a keyboard – complete the form more easily.
The goal of the PDF format is to allow users to exchange and view electronic documents easily and reliably, independently of the environment in which they were created. PDF relies on the same imaging model as the PostScript page description language to describe text and graphics in a device-independent and resolution-independent manner. To improve performance for interactive viewing, PDF defines a more structured format than that used by most PostScript language programs. PDF also includes objects, such as annotations and hypertext links that are not part of the page itself but are useful for interactive viewing and document interchange.
A properly tagged structure tree is used within each document to provide a meaningful reading order for content, as well as a method for defining structural elements role and relationship to page content. Within this tag structure, other properties such as alternative text and replacement text can be provided.
There are certain characteristics of an accessible document that can be determined upon creation as well as several different ways to produce an accessible PDF file. Searchable text allows users to utilize optical character recognition to decipher the text in a document that has been converted to a graphic representation. The fonts in an accessible PDF must contain enough information for readers to correctly extract all of the characters to text for purposes other than displaying text on the screen. Most PDF readers extract characters to Unicode text when you read a PDF with a screen reader or the Read Out Loud tool, or when you save as text for a Braille embosser. To read a document’s text and present it in a way that makes sense to the user, a screen reader or other text-to-speech tool requires that the document be structured. Structure tags in a PDF define the reading order and identify headings, paragraphs, sections, tables, and other page elements. These are just a few of the many characteristics that are included in accessible PDF files.
By working to provide all users with a more accessible PDF experience, we can work to provide more information to more people. The technology available to turn a document into a graphic for easy sharing and reliability is also available to turn a graphic image into a document that can be accessible to someone using a form of assisted technology. Information shouldn’t just be available for those who can see it. Making information accessible for all users should be priority in every aspect.