Calibre hangs and can't do anything

[vincentnoiseux]

Composite fonts are locked and can only be edited by "System". They do not show as hidden files at all, I need to open the folder in a web browser to see them...

Composite Fonts are usually used to render non available fonts with the same spacing (at least that's how they work with Adobe Acrobat).

[vincentnoiseux]

DCan't drag them out, they are locked by System...

[Starson17]

Originally Posted by vincentnoiseux

DCan't drag them out, they are locked by System...

As far as I can tell, you've got two things going on. Composite fonts are an unusual type of font. I hadn't run into that type of font file before, but it appears to be often used with large Asian font character sets. Also, the Windows\Font folder is handled differently in Windows File Explorer from most other folders. Windows File Explorer will show you what appear to be files located in that folder when there are no such files, and will lie to you in other ways, based on the fonts installed in Windows, rather than the files actually located in that folder.

You won't be able to drag out some fonts, if they aren't truly font files located in the Windows\Fonts folder.

I suspect there's something about the installed composite font file that is making Calibre unhappy. Do you know where those fonts came from? Do they appear when you try to access them via the control panel and "Fonts?"
If so, can you uninstall them temporarily that way?