How
First, you need to ensure the PowerPoint file itself is fully accessible. See the PowerPoint page for all considerations that are necessary for this. The following article from Microsoft also lists accessibility concerns for PowerPoint presentations: Make your PowerPoint presentations accessible to people with disabilities.
Be sure to include in the PowerPoint contact information that readers can use to request an alternate version of the final PDF.
Then, you will export the presentation as a PDF. The following article from Microsoft describes how to do this: Save PowerPoint presentations as PDF files.
Verify
The final PDF can be checked by using a PDF accessibility checker tool such as PAVE (PDF Accessibility Validation Engine).
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