Kindle and personal documents

Until now, only Amazon-bought content has been stored and synchronized by the Kindle system. But Amazon just wrote to me that this has now changed:

Your personal documents will be stored in your Kindle library. You can download your archived personal documents to your Kindle device(s) conveniently anywhere at any time. Your personal documents will remain in your Kindle library until you delete them. If you don't want your documents to be stored in your Kindle library you can change your personal documents settings through Manage Your Kindle. 

You can also create notes, highlights and bookmarks on your personal documents and they will be automatically synced along with last page read across various Kindle devices using Amazon's Whispersync technology. 

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