Making PDFs accessible is part of EPA's compliance with Section 508 of the Rehabilitation Act (Intranet) and it is required for all PDFs posted on EPA.gov.

PDF is a widely used format for presenting documents electronically that looks exactly like the printed originals.   PDFs are not as easy to use as text formats (e.g.; HTML and electronic documents) when using accessibility tools.

PDFs have to go through a process to make them accessible for use on the Web.  PDFs are tagged so that screen readers will be able to recognize the content and read it aloud.  Conversion of Word and other word processing documents to PDF goes more smoothly if the original document has been created to be more accessible from the beginning.   See: How to Create a Web-Ready PDF

PDF Web Standards

Standard: When to Use, Document Metadata, Info Required for PDF Sections 
Criteria for choosing PDF vs. HTML, directions on creating the title, subject, and other key metadata. EPA no longer requires or recommends the division of large PDF documents into smaller ones. If you divide one anyway there are cover page requirements.   

Standard: Linking Standards for PDF Files 
A brief description of how to add links to PDF documents. Includes several examples such as poster PDFs and using an in-line About PDF link.