Hello, @Pierre_Landry! Thanks so much for posting about this! And thanks for tagging me, @mattvaru!
The error is thrown due to an issue with the font. There are a few things that your client can try.
They can update their PDF reader or browser they’re printing from
They can update their printer driver
If they are using Adobe Acrobat to view the PDF, I do believe there is an option available to only rely on system fonts. Checking that box would also solve the issue.
In the meantime, I’m going to grab some PDF’s and do some testing and see if I can print on my end.