We have just created another video to convert any Kindle books to PDF. If the earlier tutorial video didn't work for you then please try this method.This method actually is a smart way of doing things, so as long as you can open the books with KINDLE, it should be absolutely fine to convert the books to pdf (including DRM protected e-books).
Kindle for PC 1.17 Version
[Amazon Kindle Software]
Kindle for PC is a free software by Amazon Digital Services. It’s basically used to read Kindle Books from Amazon. However, using the latest version of Kindle for PC (which can be found in the official Amazon link), we were unable to convert Kindle Books to PDF using calibre, thus, this is the older version (1.17 Version) which worked very well with Calibre for the conversion (Kindle Books to PDF).
Please check the link below for tutorial.