Accessible PDF Documents
To create an accessible PDF, it is best to start with a document (Word, Powerpoint, scanned document) that is already accessible. Please refer to the appropriate section of this website to create that.
The National Center on Disability and Access to Education (NCDAE) provides this Cheatsheet on converting Word documents to PDF. It contains instructions for the different versions of Word with helpful screen shots.
The following video describes how you can use Acrobat Pro to convert an inaccessible pdf document into an accessible one. Alternately, read those instructions here.