(for personal use of books you own)
From Amazon Website
Even if you have a registered Kindle device, you can download the Kindle book to your computer directly from the Amazon account. Log into your account Amazon Website Select Account and save your purchased book for export to USB (option near the bottom as I recall).
Then use the book reader know as Calibre
Calibre works great on linux. Calibre is one of the easiest ways to convert Kindle to PDF that also allows you to read and organize ebooks on various devices. This tool is available for all Operating Systems but I use only linux so I do not care about the others.
To convert Kindle to PDF:
Click on the ‘Add books’ option.

- Go to the Kindle book you want to convert and select it to add it to Calibre.
- Select the added book inside Calibre.
- Click on the Convert Books option.
- From the dropdown menu of ‘Output format’, select PDF.
To see the conversion, you can click on Jobs at the bottom-right corner. When the conversion is complete, select PDF and select “Save the PDF format to disk” and save it.
Open in your favorite PDF editor.