Hi,

there are some PDF files which require additional language packs such as Adobe-Japan1.
In ubuntu, these are contained in the package 'poppler-data' which is optional (but recommended) for poppler based PDF readers. In my case, it has not been installed by default.

In my case, considering the PDF document attached, there was only the "=>" glyph missing. In this case, it hadn't been immediately apparent that this was due to the missing language pack. Instead, this was my route in isolating the problem:
error in the pdf document? no, because it works in acroread
error in Okular? seemed like it at first, because 'gs' and xpdf rendered it just fine. discovered that other pdf viewers have the same problem.
accidentally checked the stdout of okular/evince to discover that both had these error messages in common:

Error: Missing language pack for 'Adobe-Japan1' mapping 
Error: Unknown font tag 'F6.1' 
Error (21281): No font in show

only after that, I found out about poppler-data; after having installed it, everything is alright now.

I propose that users should be notified about this problem via some GUI dialog within their PDF viewer (let it be up to the viewer to implement how these errors are to be displayed via unobstrusive popups), together with a suggestion to check wether language packs are installed.

As far as I can see, there is no error handling API in libpoppler, so this would have to be attacked first, before filling feature requests for the viewers...