They can also be in folders, does not matter. See also the readme.md in the /koreader/fonts folder.
The question is rather about the naming. If I copy all files into one folder superbold will be activated automatically. If I then select bold in KOReader, the font becomes a little bit thinner.
If I have only "Vollkorn-Regular.ttf" in the folder, the font is displayed normally.
|