PDF/UA Readers

PDF/UA conforming Readers and Assistive Technology (AT)

The PDF/UA-1 standard not only specifies file format requirements, but also the behavior of a »conforming reader« and »assistive technology« (AT). A conforming reader is a PDF consumer according to ISO 32000-1

(the PDF 1.7 standard) which adheres to additional provisions. AT is »software and/or hardware used by a person with a disability that provides alternative controls and/or renditions to facilitate their access to and usage of available functionality and information«. AT doesn’t usually interpret PDF documents directly, but in combination with a PDF reader. This may be done via interoperability interfaces such as MSAA on Windows. Common examples of AT are a screen reader program which presents text on the screen on a Braille device, and speech synthesis software which reads the document contents to the user. A conforming reader must correctly interpret accessibility-related information in a PDF/UA document and provide it to AT. It must support document navigation via page labels, structure hierarchy or bookmarks, and cooperate with AT by making available the following items:

  • structure elements and artifacts;
  • its user interface;
  • text in logical reading order along with the natural language of the text;
  • information about empty table cells;
  • information about the presence and names of layers (optional content);
  • names and contents of file attachments;
  • metadata and digital signature information;
  • alternate description of annotations and descriptions of form fields

A conforming AT device must consume and present the information provided by the conforming reader. It must also process artifacts, i.e. document content which is not included in the structure tree. Like a conforming reader, conforming AT must support document navigation via page labels, structure hierarchy or bookmarks.

Commercially available assistive software is expected to support the PDF/UA-1 standard in the future. The NVDA project offers a free, open source screen reader for Windows. NVDA already announced their plans to incorporate PDF/UA support in their software.