Cannot fix font problem- unrenderable font?

Carlwitthoft · 10-26-2026, 11:24 AM

I had an online service convert a PDF book to EPUB. The contents display only the "questionmark in a box" failure icon, see attached image.
I checked, and the the raw text does exist inside the html code.
There is a font listed under the name " -apple-system " . I tried to use the editor "change font" option but no change happens. I don't know whether this nonexistent font is the cause of the problem or not.
Can anyone explain how to modify the epub contents so that the text will render in a readable font?

Doitsu · 10-26-2026, 07:22 PM

Create a copy of the epub and remove Arial and/or Georgia. If that does not fix your problem, most likely the HTML files are incorrectly encoded. E.g. Windows-1252 instead of UTF-8.

Carlwitthoft · 10-26-2026, 07:34 PM

Quote:

Originally Posted by Doitsu

Create a copy of the epub and remove Arial and/or Georgia. If that does not fix your problem, most likely the HTML files are incorrectly encoded. E.g. Windows-1252 instead of UTF-8.

Never mind - it's a completely different issue. I discovered that the output EPUB renders just fine with other "reader" apps. It's Calibre itself that is suddently unable to render the text in the display window or in the "ebook-viewer.app" that Calibre uses.
If this persists beyond a reboot I'll open a separate bug report

KevinH · 10-30-2026, 08:23 AM

If you are on a Mac, and you have recently updated your OS, then this is a known issue with Apple installing a font in your system during that update that directly matches a font you once installed. This duplication is what causes the problem. It shows up when using any Qt based software.

The solution is simple. Open Apple FontBook Utility to track down which font or fonts are duplicated. Then remove the user installed duplicated fonts. FontBook can not auto fix this as the fonts that are duplicated are newly added Apple system fonts that are protected. So removing your old own installed font is the only answer. This happened to me with some old Microsoft fonts I had added long ago.

Carlwitthoft · 10-30-2026, 08:57 AM

Quote:

Originally Posted by KevinH

If you are on a Mac, and you have recently updated your OS, then this is a known issue with Apple installing a font in your system during that update that directly matches a font you once installed. This duplication is what causes the problem. It shows up when using any Qt based software.

The solution is simple. Open Apple FontBook Utility to track down which font or fonts are duplicated. Then remove the user installed duplicated fonts. FontBook can not auto fix this as the fonts that are duplicated are newly added Apple system fonts that are protected. So removing your old own installed font is the only answer. This happened to me with some old Microsoft fonts I had added long ago.

Thanks -- cleaning up fonts via FontBook did fix the problem

KevinH · 10-30-2026, 01:22 PM

Glad to hear it helped. Took me forever to figure this out last year when it first hit me.

10-26-2026, 11:24 AM	#1
Carlwitthoft Junior Member Posts: 5 Karma: 10 Join Date: Oct 2026 Device: none	Cannot fix font problem- unrenderable font? I had an online service convert a PDF book to EPUB. The contents display only the "questionmark in a box" failure icon, see attached image. I checked, and the the raw text does exist inside the html code. There is a font listed under the name " -apple-system " . I tried to use the editor "change font" option but no change happens. I don't know whether this nonexistent font is the cause of the problem or not. Can anyone explain how to modify the epub contents so that the text will render in a readable font? Attached Thumbnails

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10-26-2026, 07:22 PM	#2
Doitsu Grand Sorcerer Posts: 5,934 Karma: 24259515 Join Date: Dec 2010 Device: Kindle PW2	Create a copy of the epub and remove Arial and/or Georgia. If that does not fix your problem, most likely the HTML files are incorrectly encoded. E.g. Windows-1252 instead of UTF-8.

10-30-2026, 08:23 AM	#4
KevinH Sigil Developer Posts: 10,155 Karma: 7640000 Join Date: Nov 2009 Device: many	If you are on a Mac, and you have recently updated your OS, then this is a known issue with Apple installing a font in your system during that update that directly matches a font you once installed. This duplication is what causes the problem. It shows up when using any Qt based software. The solution is simple. Open Apple FontBook Utility to track down which font or fonts are duplicated. Then remove the user installed duplicated fonts. FontBook can not auto fix this as the fonts that are duplicated are newly added Apple system fonts that are protected. So removing your old own installed font is the only answer. This happened to me with some old Microsoft fonts I had added long ago.

10-30-2026, 01:22 PM	#6
KevinH Sigil Developer Posts: 10,155 Karma: 7640000 Join Date: Nov 2009 Device: many	Glad to hear it helped. Took me forever to figure this out last year when it first hit me.