What to expect and prerequisites
The evaluation and subsequent remediation of a PDF document is a multi-step process that combines 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 assumes you're using it. That said, the steps are pretty similar in other programs, like PDF-XChange Editor, which happens to be my personal favourite.
Automated tools like PDF Accessibility Checker (PAC) can help, but they are optional.
Metadata
Metadata is a set of data points that provides details or other information on a document such as the title, author, creation date, language, and document settings. Information found in metadata is also used by search engine indexing services and should therefore not be omitted.
In Adobe Acrobat, metadata is found in the Document Properties panel, which contains several fields 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, typically matching the document's top-level heading. Should the document not contain a heading, a short descriptive text should be used.
The author should reflect the original creator or organization, not the person who exported 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
Bookmarks are often overlooked, but they're an important navigation aid and should not be skipped.
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
The Reading Order tool affects the visual reading sequence and can also assign tags, but it does not update the tag tree directly. Review both for accuracy.
- 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, charts, and figures should include alternative text. To check, right-click the element's tag in the tree and select Properties.
- Use of colour: Do not rely on colour alone to convey meaning, and ensure text has enough contrast against the background.
- Tables: Tables should be simple, linear, and contain header cells and a caption where appropriate.
- Scanned documents: If your document was scanned or created from images, ensure it has gone through OCR (optical character recognition) so the text can be selected, searched, and properly tagged for accessibility.
- Form fields: If your PDF includes interactive form fields, ensure each field is tagged and has an accessible label or tooltip. Screen readers use these to communicate the purpose of each field.
Comprehensive testing
For best results, combine automated testing with keyboard navigation checks and real-world assistive technology testing. No single tool can detect every issue.
Adobe Acrobat accessibility checker
Adobe Acrobat includes a built-in checker that flags common accessibility issues. While not exhaustive, it's a good step before external testing.
Screen readers
Testing with a screen reader can help catch issues that may go unnoticed during manual or automated reviews.
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.
In closing
Accessibility in PDFs takes time, but even partial remediation can make a big difference. Prioritize structure, use the tools at your disposal, and always test your changes. A well-tagged document supports everyone, including those who rely on assistive technology.