openesignforms VS DeDRM_tools

I've used esignforms[0] to DIY document signing, its a bit complex to setup but what stands out to me is that the own authors do not endorse the software for legal purposes because the software has not been audited.

[0] https://github.com/OpenESignForms/openesignforms

Your kindle requires a software update to view this content? CAN'T DOWNLOAD ANYTHING DeDRM_tools#889

In theory, you should be able to do it with both Rakuten Kobo and Amazon JP. However, you might need to use a VPN to tell them that you're in Japan because of region restriction idiocy. You may also need to claim a Japanese billing address (though it may not need to be your actual billing address; some sites do require that you provide a Japanese billing address but don't actually require that it match your credit card). Out of the two, Kobo's DRM is easier to remove. I have heard that Amazon JP has not yet been affected by the recent changes that Amazon made to make it harder to remove their DRM, but it's likely only a matter of time before we won't be able to remove their DRM anymore, because it takes too much time and effort for the folks who work on such things to continue to putting in the effort.

I believe this plugin for calibre is what is used.

If you want to convert your Kindle book to PDF, and since you have a Kindle device, follow the instructions here.