In Illinois we have the Illinois Information Technology Accessibility Act (IITAA) that applies to any organization that receives state funding. This includes public education institutions such as the University of Illinois. The law states:

IITAA 15.1: "Provide natively accessible downloadable documents whenever possible.“

A document is considered natively accessible if it follows the accessibility techniques for its format. For example, if you have a Word document and have followed all accessibility rules in creating the document, and this is what you put out on the web, this would be your native document. 

If a downloadable document cannot be made natively accessible, it may be possible to provide both the original document and an equivalent accessible alternative. For example, with PDF files, due to the difficulty of making these accessible, the best thing to do is provide the information in HTML format. Thus, the document, PDF, is now being provided in an accessible format, HTML.