Magento PDF Invoice Pro extension support for Japanese language. Please follow these step to install the Japanese font for the extension..
First you need to download the font package from this url: http://www.vnecoms.com/fonts/Japanese_Font_IPAGothic.zip extract the package and upload the app folder to your magento root folder.
After you upload the font package you can use this css to display your Japanese characters.
font: 12px ipagothic;
You can put this css code to the additional css like this:
.japanese_chars{font: 12px ipagothic;}
Then from your PDF template you can use the code like this
<span class="japanese_chars">YOUR JAPANESE CHARACTERS HERE</span>
