It is definitely possible to create accessible PDF documents and forms. In most cases, you will need to use Adobe Acrobat Professional to check and correct the accessibility of your documents. The following resources describe how:

Overview

PDF Documents

PDF documents include memos, brochures, reports -- essentially any PDF that is not a form. Adobe provides the following guides on how to make PDF documents accessible:

Adobe Acrobat XI

Adobe Acrobat X

PDF Forms

PDF forms contain interactive form elements such as text boxes, dropdown lists, check boxes, and buttons. While form elements can be added to any PDF using Adobe Acrobat (resulting in what is sometimes called an "AcroForm"), the best tool to use is Adobe LiveCycle Designer, which is included with Adobe Acrobat Professional. For best results, forms should be created from scratch in Designer using the techniques described in: