It's common to find documents of all kinds turned into PDFs, usually for the convenience of the person sharing, where the aim is to have the document remain in its original format.
Accessibility
Fortunately, PDFs don't present the accessibility barriers they once did. Good, practical advice comes from JISC TechDis on how to produce accessible PDFs:
PDFs and Sharing
If it is intended that the user of the document may make amendments in the course of their re-use, then PDF may not be the correct format in which to share the document. A PDF is difficult to adapt so if the licence allows, it would be far better to leave the document in its original format before sharing.