On my Win 10 System, when I purchase a Book from Amazon, I then Start up
the Kindle for PC program.
I close any Book being read, and doing this puts me into a list of all
of my purchased Books.
As I Arrow up and down the list, I can read each title.
When I come to the New Title, I just Press the Enter Key.
Doing this Downloads the New Book on to my System, under the Fold
DOCUMENTS and then under a Sub Folder named My Kindle Books.
From what I understand, the Customer is allowed to have that Book on
three devices, say a Desk Top System, a Lap Top, and perhaps a Kindle
I doubt if you can just Copy this My Kindle Folder from the one System
to another, and have the Books available, or even recognized.
However, once you Download the Book from Amazon, you do not need to be
connected to the Internet.
Hope this Helps.