As long as it's a Kindle Fire (2nd generation or newer), then you can just transfer the files by following these instructions:
http://www.amazon.com/gp/help/customer/display.html?nodeId=200375630

Anything older, or an original kindle, you can probably use the email transfer method you can find here:
http://www.amazon.com/gp/help/customer/display.html?nodeId=200767340#s2kemail