Accessible PDF documents are getting much more imported these days, not only forced by legal regulations. The PDF Association is actively engaged on developing standards in this area, PDF/UA-1 was this first step, PDF/UA-2 is in development. Additionally helpful material, e.g. the "Matterhorn Protocol" and Tagged PDF Best Practice Guide: Syntax“ were published by the Association.
The members Klaas Posselt and Dirk Frölich got a further step and published a german book about „How to create accessible pdf files“ (official title: "Barrierefreie PDF-Dokumente erstellen", published at dpunkt Verlag). After some theoretic basics users are lead how to generate accessible PDF out of the main established authoring programs, as Microsoft Office, LibreOffice and Adobe InDesign and how to ensure the best quality of the output.
More information in German language can be found here:
The PDF Association is the meeting-place of the PDF industry. The staff of the PDF Association are dedicated to delivering the information, services and value the members have come to expect. Staff members of the PDF Association include: Duff Johnson (Executive Director) Thomas Zellmann (Managing Director) Matthias Wagner (Operations Director) Alexandra Oettler (Editor) Nicole Gauger (Editor)