One thing we see fairly regularly is manufacturers posting press releases or news announcements or other short news notices as PDFs.
However, it is generally better to post it as HTML, since:
(1) HTML can be viewed easily across devices whereas PDFs have problems loading on many systems and depend on a PDF reader being installed, accessible, etc.
(2) HTML can be more easily edited to add more information as needed rather than republishing a PDF
(3) HTML allows ones site navigation options to be displayed so a visitor can click around and spend more time on one's site.
There are certainly cases where PDFs are understandable - when the content is very long (e.g., a user manual) or where exact layout is prioritized (e.g., a marketing brochure).
But for your sake and your customers / prospects / readers sake, avoid PDFs generally.
I am posting for general information and to have something to link to when I give this feedback to companies.