I don't know anything about Quark, but it might be a mistake to use an "Esperanto" font. Esperanto's characters are included in WGL4 (a standard set of about 656 characters), so any modern high-quality font is likely to include them. If a font was specially designed for Esperanto then it's probably a pre-Unicode font that puts the Esperanto characters in a non-standard place, probably instead of some Latin-1 characters. If you find where they are then you might be able to use them, getting the text to look right, but don't expect copy and paste to work. You're probably better off using some modern font that includes WGL4.