Another author has sent me an Advanced Reader Copy (ARC) of his book as an attachment to a gmail message. He attached it in 3 different formats; epub, Kindle and Word. I opened the email message on the Kindle and downloaded the 'Kindle' formatted file to my Kindle Fire (1st generation, I believe), but when I tried to open it on the Kindle, it said the file could not be opened. Can anyone suggest how I might get it to open?
Every Kindle or Fire has an email address. You should be able to email the attachment to that address. (If you don't know it, look at Manage Content & Devices option when you hover over your account name when logged into the Amazon store.)
You should also be able to attach the tablet to your computer with a USB cord and transfer it over using Windows Explorer or similar file manager. In my Fire, books are in a folder called BOOKS. (That isn't always the case. You may have to peer at other folders to find the book titles.)