Description

The accessibility of any web content, including PDF documents, is typically evaluated against a set of standard criteria.

The most widely used accessibility criteria are those outlined in the Web Content Accessibility Guidelines 2.0 (WCAG 2.0). However, while WCAG provides some guidance for PDF documents, it’s primarily focused on HTML web content.

A PDF-specific criteria set is provided by PDF/UA, which is the international ISO standard for PDF accessibility. Because PDF/UA is highly technical, the PDF Association has created a checklist based on this standard called the Matterhorn Protocol.

The standard that you use to assess PDF accessibility will depend on your jurisdiction, your agreement with clients, etc..

WCAG 2.0

Web Content Accessibility Guidelines 2.0 are guidelines published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C) and are internationally recognized as an effective standard in web content accessibility. WCAG 2.0 is organized into four principles, each of which is further divided into guidelines, with specific success criteria for meeting each guideline. These guidelines are the backbone for supporting accessibility on the web and cover both web content and PDF documents. However, some of the guidelines and success criteria for meeting these guidelines are more relevant to HTML web content and do not apply to PDFs.

WCAG Principles

In the context of PDFs, the four principles can be described as:

1. Perceivable - Content should be perceivable to users regardless of sensory capabilities.

In order to be perceivable, a PDF document must provide text alternatives for non-text content, have sufficient contrast, and generally ensure that all content is correctly identified through the use of tags. This ensures that assistive technologies (AT) (e.g. screen readers, braille displays) can determine the correct structure and content from a file and relay it to users with disabilities.

2. Operable - Content should be operable by users regardless of how they interact with it.

In order to be operable, a PDF document must be fully accessible using a keyboard, have a logical organization and defined reading order, a document title, and clear headings, labels and links. This ensures that AT users can interact with documents regardless of whether they use a mouse, keyboard, single switch, etc.

3. Understandable - Users should be able to identify the organization and meaning of content. If user input is required, the instructions should be clear and programmatically defined.

In order to be understandable, a PDF document must be readable, consistent, and predictable. If the document contains forms, the inputs should be tagged and labelled. The document’s language should also be defined. This will ensure that all users will receive information about how content is organized, and clear instructions when their actions are required.

4. Robust - Content must be appropriately tagged in order to be compatible with a variety of user agents and assistive technologies.

In order to be robust, a PDF document must be tagged (using standard tags). This will ensure that information will be relayed to users consistently regardless of AT used.

WCAG Conformance Levels

A PDF document’s level of accessibility is determined by which of the WCAG 2.0 success criteria have been successfully met. The criteria for meeting WCAG guidelines are organized into three levels:

• Level A - basic accessibility
• Level AA - good accessibility
• Level AAA - advanced accessibility

Most digital accessibility legislation around the world targets WCAG 2.0 Level AA compliance. However, the AODA takes a more step-by-step approach, requiring first Level A and then Level AA on a timeline that depends on the type and size of the organization. However, in practice Level A is the actually the “lion’s share” of the work required to get Level AA, so in most cases it makes sense to target Level AA from the outset.

WCAG Techniques and Known Failures

Each WCAG requirement (success criterion) has a list of techniques for how to successfully meet it, as well as a list of common failures. You can find these lists by following the “How to Meet” and “Understanding” links from each of the WCAG success criteria.

These lists of techniques and failures are very helpful for knowing what to look for when deciding whether to pass or fail a page on a particular criterion.

WCAG Techniques show you examples of how issues can be properly addressed.

It is important to note that, unlike the normative success criteria, the WCAG 2.0 Techniques are informative. In other words, they do not have to be followed, and there may be other ways to meet the success criteria.

Some techniques are labelled sufficient and others are labelled advisory.

• Sufficient techniques are typically sufficient to meet a success criterion. This doesn’t mean they are required, just that if used, they are sufficient.
• Advisory techniques are suggested ways to improve accessibility. They are often very helpful to some users, and may be the only way that some users can access some types of content. Nevertheless, on their own they are not sufficient.

Known WCAG Failures show examples of things to avoid. Especially when you first start doing remediation work, it’s good practice to skim over the lists and look into the specific techniques that apply.

PDF/UA Standard

PDF/UA (where UA stands for “Universal Accessibility”) is a specification created by the International Organization of Standardization (ISO 14289). Unlike the WCAG, PDF/UA is written specifically for PDF documents. The document describes technical requirements for creating accessible PDF content.

The document describes PDF functions such as images, text form fields, and bookmarks, and defines how these functions should be used to create accessible PDFs. Conformance covers three aspects: files, readers, and assistive technology.

The files section (Section 7) is the one relevant to evaluating PDFs. This section specifies that all content within a document must be appropriately tagged using standard PDF tags, outlined in PDF 1.7 standard ISO 32000, and organized into a structure tree that accurately reflects the content, structure, and order of the file. This section also covers specifications that mirror WCAG’s guidelines such as requiring that information be conveyed through more than just visual means, avoiding flashing content, and identifying document titles and language.

The Matterhorn Protocol

PDF/UA is a highly technical and copyrighted document, which is also hidden behind the ISO paywall. In order to aid compliance, the PDF Association created a checking model for PDF accessibility based on PDF/UA called the Matterhorn Protocol. The protocol consists of 31 checkpoints and 136 failure conditions. Of these, 87 can be determined automatically, 47 require human judgment and two have no specific tests.

Comparing WCAG and PDF/UA

WCAG 2.0 and PDF/UA are complimentary, however, conformance with one does not automatically mean conformance with the other. The most important accessibility issues are covered by both sets of criteria. Because PDF/UA has been written specifically for PDF content, compliance with this set of guidelines is likely to result in more accessible PDFs. However, compliance with either standard will ensure a high level of PDF accessibility.

Some automated accessibility checkers, such as PAC 2.0, use PDF/UA and the Matterhorn Protocol to evaluate PDFs. Other checkers, such as the CommonLook PGA plug-in’s accessibility checker, allow you the option of choosing which set of criteria to use for evaluation. If you are evaluating a document against a specific set of criteria, ensure that you are using the appropriate checker and selecting the applicable settings.

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Task

Read through the WCAG 2.0 and identify the criteria and techniques relevant to PDFs.

List at least five criteria or techniques here, ensuring that the "Is this for an assignment?" dropdown is set to the name of this lesson.

Tip: Look through lists of techniques in the ‘How to meet’ section for different criteria. Most techniques specify the context in which they should be used, such as HTML, PDF, ARIA, etc. Some techniques are general and do not have a specific context, these can apply to all contexts, including PDFs. Familiarize yourself with all techniques that apply to PDF documents.

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