chm files are basically html files packed into an archive.
unpacking them should be possible, but
archmage file.chm output
“Segmentation” faulted.
lsb_release -a; # tested on No LSB modules are available. Description: Debian GNU/Linux 10 (buster) su - root apt update apt install xchm
then in caja (or other file explorer) r-click-the-file-> open with xchm
even comes with cross os support! (lin, win, osx)
the GPL licenced src is here: https://github.com/rzvncj/xCHM
the author does not have any access anymore to: https://sourceforge.net/projects/xchm/ (someone else restored the page, might be scam!)