In the spirt of old hacker ‘philez’ - this is a first in a series of ‘how-to’ regarding
some common things -
lifted from the slade knowledge base
https://www.ucl.ac.uk/slade/know/2979
and here
https://www.mobileread.com/forums/showpost.php?p=3471461
1 - secret sauce is that you must use an older copy of kindle for this to work witrh PC downloaded files
https://archive.org/details/kindle-for-pc-1-17-44170
1b - aternatively you can go here:
https://www.amazon.com/hz/mycd/digital-console/contentlist/booksAll/dateDsc/
use the ‘download & transfer via USB’ option under ‘More Actions” the key needs to be setup as the serial number for that device not all files can be downloaded this way
this plugin most likely DL inside calibre - but here JIC
3 - install this into calibre (deDRM)