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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. There do exist many libraries that leverage XML to create PDFs, but these libraries compile to the 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 generally 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 documents files instead, since further revisions would benefit from those accessibility improvements.[1]
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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
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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.
Word
Microsoft Word
InDesign
Adobe InDesign
Acrobat
Adobe Acrobat ProThe 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.
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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.
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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.