Last update: August, 2020, please let me know if you find the article out-of-date.
Disclaimer: Removing DRM from Kindle ebooks, changing format, or reading them on another device other than Kindle or official Kindle app is against Amazon’s T&C.
What is DRM?
If you buy ebooks from Amazon, checkout books from Amazon Unlimited or local library through kindle, most likely it comes with copyright protection called Digital Rights Management, aka, DRM.
Why remove DRM?
DRM prohibits you from copy it from one device to another, and you can only read it from Kindle or official Kindle app. If you want to read it on another device, or any app/device other than Kindle, for example, Sony or Kobo ebook reader, it won't read the files you copied over. Fortunately, Kindle ebooks can be deDRM or even converted to ePub very easily.
Open Calibre, go to Preferences - Plugins - Load plugin from file.
Books from Kindle for PC located at C:\Users\YOUR_USER_NAME\Documents\My Kindle Content
Drag azw files to Calibre
Select AZW3/ePub format
AZW3 is Kindle format, so the output files can be copied over to another Kindle device.
And most ebook readers support ePub format.
Depending on the numbers of pages of ebook to be converted, it takes tens of second to several minutes to finish the conversion. And that's it!