PDF Accessibility Overview
PDF General Knowledge
In general, the PDF format is known as a "destination" file format, meaning there isn't a good way to interact with the compiled code that generates a PDF directly. The PDF format which is considered mostly to be "machine-readable" only and isn't easy to edit directly.
Thankfully, there is other software like Adobe Acrobat Pro that enables us to improve the general accessibility of PDFs. This workflow could be considered "repairing" the PDF, but ultimately the generally accepted advice is to focus on the "source" document instead. For example if the PDF in question is created in software like Microsoft Word or Adobe InDesign, it is preferred to add the accessibility fixes in question to those source files instead, since further revisions would benefit from those accessibility improvements.[1]
Auditing PDF Accessibility
PDF accessibility auditing looks a lot like web accessibility auditing, since in both cases we want to achieve a document that allows everyone to be able to parse the content. Like web accessibility we want to have strong structure, easy readability, and extra tagging for assistive technology. Adobe even suggests the WCAG standards as a jumping-off point for PDF accessibility, so it should be easy to frame a PDF accessibility audit much like a web one, with the largest difference being the tooling used to complete the testing.
Guidelines
Headings
Like in HTML accessibility, heading structure is deeply important to the understandability of your content by assistive technology.[2] Using a PDF tool to view the structure or listen to it with voiceover technology is key.
Contrast
Contrast among readable text is important for all sighted users. A good rule of thumb is to test the colours of the document against a WCAG AA contrast checker.[3]
Alternate Text
Alternate or alt text is important for any meaning that may be conveyed by non-text assets. For example, images, video, or other multimedia files should all have text summaries attached or methodologies for describing content that assistive technology can interact with. Most PDF creation tools will provide their own methodologies for adding this so the results may be different from PDF to PDF but the key is to ensure assistive technologies can access the same information and meaning across the board.
Copyability
The "copyability" of the text is important to how many users will parse a PDF. If the text is not copyable or editable, many techniques for understanding are disabled. Many users will copy text into custom readers and disabling this will prevent users to use a solution of their choice. Some say they need their PDF to be "secure" as an excuse to disable text copying, but in this case "secure" is synonymous with "inaccessible" so the choice is fairly binary.
Links and Navigation
Allowing the user to understand where they are at all times is an important angle to consider. Like web accessibility, being able to understand the context of where you are in the document is important for both sighted and non-sighted users. This means the document should be laid out in a simple way but also have tagging compatible with assistive technology. All headings and links should be semantic in that they provide context on their function and place in the document by default.
Animation & Motion
When using advanced PDF features like video or moving GIFs, it is important to consider certain motion disabilities. Unlike the web, there may not be a way to outright disable the animation like prefers-reduced-motion queries, so it is important to consider the need for graphics that autoplay or convey meaning. Instead ensuring that you have static alternatives like text summaries is preferred, and skip any un-needed pomp and circumstance.
Creating Accessible PDFs
As mentioned above, creating an accessible PDF usually starts with the source document which created it. We'll outline a few common practices and the way to edit a compiled PDF if all else fails here. One side-effect of the plethora of ways you can create a PDF is that some PDF creation suites might not have the tools to add some of these recommendations natively, and in those cases you'd have to similarly remediate them in post compilation software like Acrobat.
Acrobat
Adobe Acrobat Pro is likely the most complete suite for checking and amending PDFs.
Automatic Testing
Acrobat Pro will give you an automated overview of the document’s accessibility health, like lighthouse or AXE browser tools. The following guide will produce a report of actionable fixes.
Go to tools
Add the Accessibility Tools Shortcut to your tool bar
Click the Accessibility Tab on the right
Select “Accessibility Check”
Now, on the left of the document, you should see a tree with what the parser thinks the document structure is and any issues it may have caught
Remediation
In Acrobat Pro, you can remediate most issues using the tools available within the Accessibility suite.
On the left is the bookmarks, or what the PDF viewer interprets the document structure to be.
And on the right hand side, you can add alternative text to elements that don’t have them.
Batch Fixing Many PDFs
While there aren’t too many solutions for auto-fixing a large number of inaccessible PDFs, Acrobat Pro provides a method to fixing many PDFs at once.
Under tools select “Action Wizard”
From the actions available select “Make Accessible”
Under the “Files to be Processed” section, select add files and add all relevant PDFs
Select start and the process will run. A number of question boxes will pop up related to document tags and titles. Fill in all relevant data as prompted and the software should handle the rest
Pave
Pave is an alternative to Acrobat for quickly fixing PDFs under 5 megabytes. It will provide a list of issues and an interface to remediate most problems.
The tasks and properties tabs lay out issues that affect the whole document whereas issue details break the document down into page-by-page issues. Complete all fields in these areas and download the document and you should have an accessible PDF.
Fixing Google Slides Exports
One issue that we’ve faced is a Google Slides presentation exporting without tags and corrupting when tags are added. Should this issue arise again, you can remediate the issue by exporting as a Powerpoint .pptx file, and then exporting as a PDF from Powerpoint. The web version is suitable for this.