Warn if fallback font is used (fontconfig)
Some PDFs do not embed all fonts. For example D050000L ZapfDingbats font is commonly used in governmental or bank documents.
Unfortunately, if the font can't be found by fontconfig a fallback font may be chosen that does not support all characters contained in the PDF. For example https://bugs.kde.org/show_bug.cgi?id=433979 https://bugs.gentoo.org/716856 report an issue where this results in missing glyph or transparent character to be displayed instead of a "
poppler should provide hooks to warn the user about such problems. For example, qt5/demos/poppler_qt5viewer should create a warning dialog. Downstream applications such as Okular or Evince should be provided hooks based on which they can create warning dialogue.