I would think since no one is making any money and you are doing for yourself it wouldn't be any different that recording a TV show to be watched later or even a movie to be watched a number times in the future.

I have thought about doing that with some older books that aren't on eBook or Audible. The poor paperbacks are falling apart and some can't even be purchased any longer.

Some of my friends have written stories and shared them with me. Kindle has an app or had one anyway (it still shows up on my computer but I haven't used it in a few years) that your could upload a document onto your Kindle. I have a number of my friends stories. They aren't professional writers but like to write and I like what they have written. It is simpler to carry my Kindle around that a bunch of papers I've printed off my laptop.