Kindle / Remarkable E-book Compatibility

I was recently given a hand-me-down Remarkable 2 tablet, which is good because I would never have spent on money it - not because it's not good, but because it's $600 for essentially an e-ink sketch pad. I wanted to mark up some e-books I own, but they're from Amazon, so I had to figure out how convert them to a format the Remarkable would support. UPDATE: Amazon has removed the option to download…