A quick tip that might help others (or me, the next time I forget)…
I found that Evince, Ubuntu’s default PDF viewer, doesn’t display Japanese characters, at least on my non-Japanese system. After a quick search it seems the answer is nice and simple – install the poppler-data package.
So, either use the Synaptic Package Manager or the following terminal command:
sudo apt-get install poppler-data
And that’s it!
This should work for displaying Chinese and Korean characters as well.