KFX -> PDF, need some help

Operating system: Linux Mint 19
Desktop: Cinnamon 3.8.9
Reader: Amazon Kindle Paper White ( about 2 years old )
Calibre: 3.21.0+dfsg-1 build 1
DeDRM plugin 6.63
KFX Input plugin 1.17.1

I saw the sticky, but not having done anything with my ereader, but read I didn't understand most of it.

I'm trying to take an ebook off of my Kindle Paperwhite and make a PDF copy.

I copied the *.kfx file off of my Paperwhite via a USB cable to a place on my computer. I installed the DeDRM and KFX Input plugins.

I clicked "add books" in Calibre, picked my kfx file, it got into calibre okay.

I then right clicked the listing for the book, picked convert, picked PDF as the output format and got an error message telling it is locked by DRM.

Am I missing a step?

Thanks for any clues.