[NTG-context] troubles with latin modern and mutool

[Damien Thiriet]

Hello,

I am facing some unexpected troubles while splitting my lessons to send
them to my pupils.
My idea was to use mutool draw to extract only the pages of my
presentations relevant to my lesson of the day.
Unfortunately, when I do for example

mutool draw -o file-beginning.pdf file.pdf 2,5
This extracts pages 2 to 5 
I got those warnings

warning: cannot create ToUnicode mapping for GWKFXT+LMSans10-Regular

The resulting pdf is perfectly readable on my computer, but some pupils
claimed they received garbage encoding and an unreadable pdf (on OSX at
least).
This might be a mutool bug, so I don't send any MWE.

Do you know any alternative to mutool draw to send clean pdf from pages
of my presentations?
Regards,

Damien Thiriet