Hi Pilou,

you made so far everything correct, but you missed to download and install
ImageMagick ... :-) Better i put next time also links for software i mention
in my postings ... , sorry!

The convert command is part of ImageMagick.

https://imagemagick.org/index.php

And for me there is no problem to use encryption tools, because i live
in Germany. I remember that a couple of years ago that for example
in France encryption was not allowed, but the French law has changed
in this respect, IIRC.

Best regards
Stefan