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 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: Alexandra Oettler (Editor) Betsy Fanning (Standards Director) Duff Johnson (Chief Executive Officer) Matthias Wagner (Operations Director) Nicole Gauger (Editor) Peter Wyatt (Chief Technology Officer) Thomas Zellmann (PDF Evangelist)