To be honest, there’s a few good comments linking to scripts and methods here to batch convert them on a windows pc/vm. That’s the best way to go.
To add on to their comments. If you’re just interested in preserving them then maybe printing them to pdf, specifically pdf/a, would be my approach once you got them opened.
Waaaaay better.
Restic allows you to make dedupe snapshots of your data. Everything is there and it’s damn hard to loose anything. I use backblaze b2 as my long term end point / offsite… some will use AWS glacier. But you don’t have to use any cloud services. You can just have a restic repository on some external drives. That’s what I use for my second copy of things. I also will do an annual backup to a hard disk that I leave with a friend for a second offsite copy.
I’ve been backing up all of my stuff like this for years now. I used to use BORG which is another great tool. But restic is more flexible with allowing multiple systems to use a single repository and has native support for things like B2 that BORG doesn’t.
We also use restic to backup control nodes for some of supercomputing clusters I manage. It’s that rock solid imho.