On your site, the Kindle version of the manual is in in the outdated mobi format. I think that the latest format is something like azw3
When I sent it to my Kindle, I received the following email from amazon
thank you
Dear Kindle Customer, Thank you for using the Send to Kindle service to send personal documents to your Kindle library. We noticed that the following document(s), sent by you at 03:30 PM on Tue, Feb 14, 2023 GMT are in MOBI (.mobi, .azw) formats: * DEVONthink Manual.mobi
We wanted to let you know that Send to Kindle will soon remove the ability to send MOBI (.mobi, .azw) files to your Kindle library. Any MOBI files already in your library will not be affected by this change. MOBI is an older file format and won’t support the newest Kindle features for documents. Any existing MOBI files you want to read with our most up-to-date features for documents will need to be re-sent in a compatible format. Compatible formats now include EPUB (.epub), which you can send to your library using the new Send to Kindle for Web, the free Kindle app. We will be adding EPUB support to the Send to Kindle desktop app for PC and Mac. If you have any questions, please visit our help page or contact our Customer Service team. Regards, Amazon Kindle Support
