Rhonda and her group have done a bunch of work on using best practices in Word to create accessible PDFs from reports. This is the corresponding info for InDesign CS4.
From the PDF’s intro (emphasis added):
Can you read this document with your eyes closed? For people with visual disabilities, that’s a challenge they’re faced with everyday. Fortunately, you can use Adobe InDesign CS4 to make an accessible PDF document. You do this by adding “under the hood” features that don’t affect the look of your pages, but do allow screen readers and other assistive devices to function properly.