But apart from that it should be perfectly straightforward :) I know in Acrobat reader it has/had an option for showing 'greek text' below a certain size. Which isn't greek, just a way of saying 'there is text here but I can't accurately draw it'. So I guess some part of your system perhaps isn't giving the rest of it the credit it deserves for its ability to render text, and is just thinking 'Nah! Impossible! I won't even try!'

Someone who actually knows about this stuff can possibly offer a slightly more plausible explanation...