mupdf doesn't render glyphs with a size > 1000 Px. This is relevant for banners etc. There is an error message like this: font size too large (1620), not rendering glyph Other PDF viewers have no such limitations, and I don't think the PDF spec sets a maximum font size. According to the README mupdf should render all valid PDF content.
*** This bug has been marked as a duplicate of bug 692103 ***