About the serif font.
I renamed my epub file to zip, opened it, and had a look a the
stylesheet.css file with a text editor (gedit with Linux). It was a pretty long one but I quickly realized that close to Times New Roman there was always written sans-serif.
I searched and replaced 22 occurences of sans-serif with serif, saved and made a new epub.
But when I opened the file on my PRS-505? it was declared "invalid file"...
Had a good dinner then.
Except dinner, any idea?