This site 'provides extensive information regarding the production of accessible PDFs using InDesign.'
'Adobe® InDesign® CC software supports accessible cross-media publication, allowing you to export InDesign documents to ePub, HTML, or accessible PDF. Reduce the time it takes to create PDF documents that people with disabilities can use more effectively. Apply accessibility features within your InDesign document, rather than having to make major changes in Adobe Acrobat® software. PDF tags, alt tags, and the content order you assign stay with the document as you revise it.
Used in combination with Acrobat for touch-up of the exported PDF files and Adobe Dreamweaver® software for HTML output, users can achieve maximum accessibility for the exported content.'