In the default the Arabic font is not installed to our PDF Invoice Pro magento extension. Please follow these step to install the Arabic font.
First you need to download the font package from this url: http://www.vnecoms.com/fonts/Arabic_Font.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 Arabic characters.
font: 12px tahoma-arabic;
or
font: 12px arabtype;
You should put this css code to the additional css like this:
.arabic_chars{font: 12px tahoma-arabic;}
Then from your PDF template you can use the code like this
<p class="arabic_chars">YOUR ARABIC CHARACTERS HERE</p>
