mPDF can't access private files for image creation

Hi, making private file public (even temporary) can be considered a vulnerability.
I would say better keep it not working instead of introducing security issues.

An option we should consider here - convert private file to base64 and pass it to mpdf as "data:"
This is the issue for the mpdf library, not for this module, as this seems to be only partially working in a couple of specific versions of mpdf,
see the related issue on mpdf issues queue:
https://github.com/mpdf/mpdf/issues/1687

One more possible option can be found in Entity Print module:
https://www.drupal.org/project/entity_print/issues/3111731 →