Accessible PDFs
Though PDF files are becoming more accessible, it is still important that you avoid requiring surfers to download and open a document to access information when the same information could be offered primarily as a Web page with html. PDF, MS Word, PowerPoint, and text documents should only be offered as an alternative to existing html pages containing the same content-not as the only source of that content. See this tip for more information.
Accessible tables
Tables should only be used for tabular data or in rare cases where a desired layout effect cannot be acheived without. The problem is that assistive devices read table data from left to right, row by row. Therefore, table column headers are not repeated for each row or cell, making the audible version of the table unintelligible.