Re: OOC thread
The PDF format is incredible diverse and rather complicated, the definition document is a tomb in itself (I used to work for a company that produced document management and produced a tool to reverse engineer PDFs and add in a text layer from OCR, or swap images for higher compression version).
I suspect that the rune font is embedded within the PDF, if it was added as a font, or as images. Either way, the PDF spec allows the use of pointers to characters/images, rather than repeating them in location (saves on size) and what you see is in fact normally an interpretation of a load of data, i.e. only in very simple PDFs is a character/image actually there in the place on the page that you see it, rather the reader is displaying it there after interpreting everything.
My guess is that either the PDF isn't quite to spec, or the readers are not quite interpreting the spec properly.