Nowadays they mail .docx around, haven't seen a .doc in a long time. I'm a software dev on Linux and haven't even LibreOffice installed. I tell the sender to please send it to me as .pdf. I write docs in markdown on GitHub (the company I work for uses GitHub, make of it what you will).

PDF is easy to read. It's a ridiculous document format for the purpose of internal sharing and reading, but it still works well for that purpose.

But PDF is not really optimized for editing or collaboration, and the tools available on Linux especially are limited.

I like PDFs when I trust them, but I’m always a bit wary receiving them from random people. Don’t they support embedded scripting?

I’d like a format that is like PDF, but markup only.

Well, my viewer doesn't support embedded scripting. :D