What to expect and prerequisites
The evaluation and subsequent remediation of a PDF document is a multi-step process that combined several automated and manual checks. This guide provides a high-level overview of metadata, tags, bookmarks, and general structure, as well as basic semantics and other best practices.
Viewing and editing PDF tags isn't something only Adobe Acrobat Pro can do, but since it's such a widely used tool, this article assumed you're using that. That said, the steps are pretty similar in other programs, like PDF-XChange Editor, which happens to be my personal favourite.
Automated tools such as PAC 2021 will also be used but can be skipped entirely if desired.
Metadata
Meta data is a set of data points that provides details or other information on a document such as its title, author, composition date, language, as well as a document's settings and options. Information found in meta data is also used by search engine indexing services and should therefore not be omitted.
In Adobe Acrobat, the meta data is found in the Document properties panel where there are several data points to validate or populate. To view the panel, open the File menu and select Properties from the dropdown list.
Description tab
In the Description tab are the document's title, author, and keywords. The title should be unique and descriptive to the document, and is typically the same as the top-level heading. Should the document not contain a heading, a short descriptive text should be used.
The author is the original document author's name or organization rather than the person who's converted the document to PDF. While optional, the Subject and Keyword fields should be populated as they are used by search engine indexing services.
Initial view tab
In the Window options section is the option to either display the document's file name or title in the title bar. This should be set to display the title that was previously set in the Description tab.
If the document contains bookmarks, the Navigation Tab option should be set to Bookmarks Panel and Page. Otherwise, it can be left to Page only.
Advanced tab
Critical to screen readers, the document's language is set in the Advanced tab. Ensure this field is populated either with the preset languages or by using the IANA language tag such as en-CA or fr-CA.
Bookmarks
Often overlooked, bookmarks are an invaluable navigation aid and should not be omitted.
The general rule of thumb is that every heading should have a matching bookmark. If your document contains more than a handful of headings, is divided into sections, or otherwise spans multiple pages, it would likely benefit from the addition of bookmarks.
Tags
Tags are semantic markers that provide the non-visual structure of a document and arguably the most important part of an accessible PDF. Every element is assigned a tag that provides information about the type of content enclosed within it.
In addition to providing structure, tags also serve as a reading order for a document. The tag tree is a sequential list of elements that screen readers follow.
The tag panel is not available by default and must be enabled in the Navigation Panes menu.
- View
- Show/Hide
- Navigation Panes
- Tags
Validating tags
The process of navigating through tags is referred to as walking the tag tree. Select the first element in the list and press the down arrow to move to the next element. As you move down the tree, ensure every element is tagged and accurately represents the content found within.
Managing tags
In some instances, it may be necessary to add, modify, or shuffle tags in the tag tree. Managing tags involves the Reading Order tool to select and tag elements.
- View
- Tools
- Accessibility
- Open
If an element is tagged incorrectly it can be corrected by typing in the correct tag manually or by right-clicking the tag and selecting Properties from the context menu. In the Properties panel, the correct tag can be selected from a list.
To add a tag using the Reading Order tool, click and drag around an element to create a selection. Assign the selection a tag by pressing the appropriate button in the Reading Order panel.
Other content and design considerations
Beyond a document's structure, there are several things to keep in mind when it comes to designing accessible documents in general that also apply to the PDF format.
- Page numbering: Page numbers found in footers must match the PDF reader's page numbering scheme. If the document displays "Page 8" in the footer, the expectation is that this matches with "Page 8" in the PDF reader's navigation as well.
- Alternative text: Images, graphs, charts, and figures should provide alternative text versions for assistive tools. To verify if an element has alternate text, find the element's tag in the tree, right-click, and select Properties from the context menu.
- Use of colour: Ensure your document does not rely on colour alone to convey information, and that the colours used provide enough contrast.
- Tables: Tables should be simple, linear, and contain header cells and a caption where appropriate.
Other comprehensive tests
Screen readers
The use of a screen reader will highlight potential issues that may have gone unnoticed in the tags or missed by the automated validation. Issues such as non-standard characters, a broken reading order, or inaccurate alternative text can easily be missed during other steps.
PDF Accessibility Checker
The PDF Accessibility Checker (PAC) by the PDF/UA Foundation is a free and powerful validation tool against the WCAG or Universal Accessibility standards.