> This happens when there are multiple PDFs embedded in a single PDF file.
quoted text
> I remember reading a Ghostscript bug about this (could probably find it
> again if I had the exact error message), but unfortunately Mupdf still
> doesn't support it.

Here is the Ghostscript bug:
http://bugs.ghostscript.com/show_bug.cgi?id=690422

From here it looks like you might be able to get it with gs after all.

This forum thread claims that Okular can view PDF portfolios as well:
http://www.linuxquestions.org/questions/linux-software-2/pdf-portfolio-833748/

--
Anthony J. Bentley