Portable Document Format (PDF) documents have become widely used on the web. They are great for print but poor for accessibility.
Not everyone has Word and it is poor for accessibility compared to well coded HTML.
Always provide documents in HTML form unless totally unpractical to do so:
Provide PDF and Word in addition to, not as a replacement for
For long documents that are intended for printing provide an accessible HTML summary
PDF accessibility: PDFs can be made more accessible, but will never be as accessible as HTML. In general it is much easier to make an accessible HTML version of a document, than try to make the PDF more accessible.
Practicality: Much of your existing content may be in PDF form. It may be impractical to convert all of this to HTML.
The priority must be for important and frequently visited information to be converted. All new content should have a HTML version.