Documents sent through Amazon's Personal
Document Delivery Service are now automatically archived in your Kindle Library
(you can control this from the Manage Your Content and Devices page in your Amazon account).
So even if you originally sent the file to a different Kindle device or app,
you can re-send to another device all within your Amazon account.
Go to your Manage Your Content and Devices page in your Amazon account, then under Your Content filter to see Docs and if the
title appears here, click on Actions and then click on "Deliver" and select the Kindle
device/app you're using. Your device will sync wirelessly and the title will
show up on your Kindle device or app.