Title: Guidelines for Accessible PDF Documents
Course: Web Accessibility MOOC for Educators > Section: Creating Accessible MSOffice and PDF Materials

Portable Document Format (PDF) files are created in a variety of ways, from a variety of applications, and for a variety of purposes. Achieving the desired accessibility goals for an individual PDF file requires understanding the nature of the PDF and its intended use. The PDF format is the native file format of the Adobe Acrobat family of products. The goal of this format and these products is to enable users to exchange and view electronic documents easily and reliably, independently of the environment in which they were created. PDF relies on an imaging model to describe text and graphics in a device-independent and resolution-independent manner. To improve performance for interactive viewing, PDF also includes objects, such as annotations and hypertext links, that are not part of the page itself but that are useful for interactive viewing and document interchange. PDF Accessibility Overview. (n.d.). Retrieved June 3, 2015, from Adobe PDF Accessibility Overview

The PDF format is a destination file format and PDF files are typically created in some other application. Optimally, document accessibility should begin in the native document format. For example, many documents are created in a word processing or desktop publishing application, and then exported as PDF documents. There many things that can be done in native document applications to support accessibility, such as adding alternative text for images; defining structural headings, lists, and data tables; providing document language; and setting document properties such as titles.

Characteristics of Accessible PDF files

Accessible PDFs include but are not limited to the following characteristics:

Searchable text

A document that consists of scanned images of text is inherently inaccessible because the content of the document is a graphic representing the letters on the page, not searchable text. Assistive technology software cannot read or extract the words in a graphical representation. Furthermore, users cannot select or edit the text or manipulate the PDF for accessibility. Scanned images of text must be converted into to searchable text using optical character recognition (OCR) before addressing accessibility in the document.

Fonts that allow Characters to be Extracted to Text

The fonts in an accessible PDF must contain enough information for Acrobat to correctly extract all of the characters to text for purposes other than displaying text on the screen. Acrobat extracts 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. This extraction fails if Acrobat cannot determine how to map the font to Unicode characters.

Interactive Labeled Form Fields with Accessible Error Messages and No Timing

Some PDFs contain interactive forms that people fill out using a computer. To be accessible, form fields must be interactive; that is, a user must be able to enter values into the form fields. Interactive PDF forms also have a defined tab order which allows users of assistive technology to use the Tab key in order to progress from one form field or interactive control to the next in a logical manner. Refer to the document Adobe® Acrobat® Pro DC Accessibility Guide: Creating Accessible Forms for complete details. Forms must provide identification, give tips on proper completion, and prevent errors. Form entry should not be timed unless the user can request more time.

Other Interactive Features: Hyperlinks and Navigational Aids

Navigational aids in a PDF — such as links, bookmarks, headings, a table of contents, and a preset tab order for form fields — assist all users in using the document without having to read through the entire document, word by word. Bookmarks are especially useful and can be created from document headings. These features can be accessed using the keyboard without relying on the mouse, and allow for multiple ways for users to navigate content.

Document Language and Title Indication

Specifying the document language in a PDF enables some screen readers to switch the current speech synthesizer to the appropriate language, allowing correct pronunciation of content in different languages. Providing a document title allows the user to locate and identify the document.

Security that will not Interfere with Assistive Technology

Some authors of PDFs restrict users from printing, copying, extracting, editing or adding comments to text. The text of an accessible PDF must be available to a screen reader. Acrobat’s security settings can be set to protect document content while not interfering with a screen reader’s ability to convert the on-screen text to speech or Braille.

Document Structure Tags and Proper Reading Order

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. Document structure tags in a PDF define the reading order and identify headings, paragraphs, sections, tables and other page elements. The tags structure also allows for documents to be resized and reflowed for viewing at larger sizes and on mobile devices.

Alternative Text Descriptions for Non-Text Elements

Document features such as images and interactive form fields cannot be understood by the user of a screen reader unless they have associated alternative text. Though link text is available to screen reader users, it is possible to provide more meaningful descriptions via replacement (actual) text. Alternative text for images and tooltips can aid many users, including those with learning disabilities. Equivalents for multimedia, including any audio and video elements, must also be present.

Other Accessible Document Characteristics

There are additional characteristics of accessible documents including:

- No reliance on color or sensory characteristics alone to convey meaning
- Use of color combinations that provides a sufficient degree of contrast
- Controls for audio
- Use of text instead of images of text
- No use of flashing or blinking elements
- No focus changes without user initiation
- Consistent navigation and identification of elements

Accessibility Overview. (2011, November 11). Retrieved July 21, 2015, from http://www.adobe.com/content/dam/Adobe/en/accessibility/products/acrobat/pdfs/acrobat-x-pdf-accessibility-overview.pdf