Kindle e-books purchased from Amazon usually cannot be legally converted in format so that they can be read on readers from other manufacturers. The e-books sold by all other providers in EPUB format, on the other hand, can very well be converted to Kindle format as long as they are not protected by digital rights management (DRM).
The open source program Caliber, a management and library software for e-books, performs such a conversion. And now Amazon has also announced that it will convert the EPUB format to Kindle format for its customers if required.
By email to the Kindle
To do this, one needs to email the DRM-free EPUB books to an email address assigned to the Kindle reader. This feature is called Send to Kindle. The e-mail address of your own Kindle reader is in the Amazon customer account.
This also works with text documents (doc, rtf, txt), PDFs, websites (html), image files (jpeg, gif, png, nmp) and e-books in Mobi format. However, mobile support is scheduled to expire at the end of 2022. However, Mobi books that have already been loaded into the Kindle library should remain readable beyond this point in time.
Transfer apps not ready yet
If you want, you can also use the “Send to Kindle” apps instead of the e-mail transfer to bring files in all the formats mentioned to your Kindle device. Exception EPUB books: According to Amazon, the apps should not be able to process them until the end of 2022.