You can easily add Kindle books to Calibre for automatic DRM removal without using the Kindle App at all. To do so, you need to have a Kindle reader or a Kindle Fire tablet.
The first two steps, you will only do once. They prep Calibre to accept Kindle books without Kindle App. Once Calibre has your Kindle device’s serial number, it will open Kindle books every time.
a. Go into your Kindle’s Settings.
b. Click on Device Options, then click on About your device.
c. Write down the serial number of the device. There are only zeroes (no letter O).
a. Open the Calibre App on your PC.
b. On the top menu, go to Preferences. Click on Plugins.
c. On the Plugins screen, click on Show only user installed plugins.
d. Choose File Type, then highlight DEDRM (by Apprentice Alf).
e. At the bottom of the screen, choose Customize Plugin. A long list of
supported devices will show up.
f. Select Kindle eInk eBooks. On the popup screen, enter the serial number you wrote down, no spaces between the number groups. Click on Close, then click on OK.
a. Go to your online Amazon Account Admin. This should be on the top right corner of your Amazon page, where it says Hello, name, Account & Lists.
b. Scroll down to Content and Devices. Select Books.
c. Find the book you wish to transfer. On the far right side of the screen, click on More Actions.
d. Select Download & Transfer via USB. The next screen will show a list of your Amazon reader or reading devices.
e. Select your Kindle device, the one whose serial number you wrote down. A message will show up telling you the download to your device was successful, immediately followed by your PC’s download screen.
f. Select your PC’s Downloads directory and click on Save. Your book is now on your computer.
Now you can add the book to Calibre.
a. Go to Add books. Choose Add books from a single folder. You will chose your Downloads directory, where your book was downloaded.
b. Highlight the book, click on Open, and the book will be imported into Calibre free of DRM. Now you can convert it to your format of choice using Calibre.
The next time you want to transfer a book to Calibre, you only need do steps 3 and 4. This method, in my opinion, is the easiest since you don’t have to deal with two separate apps.