Maybe I’m doing something wrong but the settings are pretty basic and clear. They mention 3 fonts though they don’t indicate what each is for. I’ve changed them but there is no difference in the font displayed in the epub I’m reading. Are epubs not changed by that?
Experiment a bit. Some settings are applied only if UseFixedPageUI = true.
Which settings are you referring to?
Changing EbookUI / FontName should work (http://www.sumatrapdfreader.org/settings.html).
Unless you set UseFixedPageUI = true in which case different logic kicks in.
Also be aware the font name windows uses may be different to that seen in lists
for a similar issue see Having some font problems
Note it is NOT the filename e.g. NOT georgiai.ttf
NOR the internal Typename e.g. georgiai.ttf which shows it is Georgia (the family name)
also it is NOT what the font view reports e.g. Georgia Italic (Open Type)
if you especially want Italic it must be simply Georgia Italic (with the space)