Font replacement/missing warning (at least) when opening affected files

[LinguaOccultus]

Is your feature request related to a problem? Please describe. Yes. A file created with a custom font not installed on the system opens normally, but it does not warn you about a missing font and I just became aware of this by chance.

Describe the solution you'd like The direct opposite: there should be a warning of missing fonts at least so the user is aware of this when opening a file and can take care of this. Currenctly, text using a missing font simply uses a default/replacement one and is shown still, but in more complex diagrams or depending on your view settings or design, you do not became aware of this eventually. A font missing warning is a quite common solution to make the user notice this before sending files out, printing them or whatever else without noticing this issue, maybe. Other applications partially show more details like the affected pages or even directly go through the text like with spell checking, but at least a warning when opening the file would be nice. Maybe the text affected could be temporarily marked with a color or something (not changing the color so I have to change it back; only displaying it differently which would not be saved with the file).

Describe alternatives you've considered N/A

Additional context None.