Some of you might be interested in this Mastodon thread. It’s a bit of bashing PDFs for having poor accessibility, and some guidance on improving PDFs for accessibility.
Some people are saying they prefer MS Word over PDF for accessibility reasons. Of course the elephant in the room is that “accessibility” is an over-loaded word. It usually refers to usability by impaired people, but in the case of being generally usable to all people on a broad range of platforms, MS Word is obviously inaccessible due to being encumbered by proprietary tech by a protectionist corporation.
tl;dr there are better suited e-book formats popular with pirates
XML was made into many formats, not obly DOCX but also FB2, EPUB if you need to just store formatted text. They are light, not resource heavy, and they adapt to any custom styling – so it's ideal for both sighted and blind persons on any device. I've read FBs even before smartphones. They have their quircks and need an improvement, but there's a reason it's popular with free ebooks.
What Adobe accomplishes with PDF is selling an idea of digital books to publishers. It promises to keep the page layout fixed, unchangeable and implements a basic DRM so it's content can't be easily copied. There's also no guarantee it's a recognized text, a correctly recognized at that, not a gibberish, and due to a fixed layout may have an unobvious, erroneus formatting. Basically, if you get a PDF and rely on TTS engines, it's cat in the box, but there are no way someone is insane enough to compile any XML file entirely from pictures.
As I'm poor-ass motherfucker who don't buy digital books, for me it's obvious. But, as I said, PDFs are popular with publishers so you see them sold everywhere.
And for DOCX - until you need to edit content, all these functions and added weight are of no use, and, honestly, as a format and as a tool it's just a clusterfuck that people often use for things it's not meant too until it breaks. Still, if choosing a book format, it's too just a scrollable text that has free software to tackle.
Although I'm not a blind person myself, I hope my info helps.
edit: After reading the thread I suspect it's a little bit of solving problems we ourselves invent. Plain text is ideal as it doesn't put any restriction on usability, accesebility at all. Then we get formatting with FB2 and EPUB, then get advanced formatting, further adding decorations a blind person can't see - and we have Word, free alternatives for that, and we don't really lose much yet. And then we have PDFs with paid editing (unless you can code) that may as well be just a scan, a picture - the most popular way of using PDF documents I know. It's great that someone makes and maintains the tools needed to access the most sold format accessible, but it seems if there was indeed care for that, PDF should've been deprecated long ago. It creates obstacles on the way to sell itself, and then there are some anti-tools to market it as a non so hostile thing. And as Adobe is built around creating software to edit visual content and inventing new technics to lock out a user from tools, they don't look like friends to blind folks. Even compared to Microsoft who had some push in accessibility with their controllers after CEO happened to have a child with disability.
I dislike Microsoft Office as much as anybody else, but there’s a certain privilege of being able to conveniently use different (FOSS) tools and technologies that’s often ignored in these discussions.