I tend to write in markdown. If someone needs a Word Doc/docx whatever format they're using these days, I use pandoc to generate it. If someone sends me a docx file, I can read it with my choice of software without paying the MS tax. On the very rare occasion someone sends me a docx file that they need me to edit and send back to them, I'll do it with whatever is handy and if they complain I messed up their formatting or whatever I can blame Word bugs.