Hi Lori ,
Using the typewriter tool you can simply add the text.
For editing the pdf you have to click on Edit button. While doing so if it’s prompting for Korean language support package it means that you do not have the necessary fonts / language pack installed on the machine.
Please refer to the following link to download the Korean Language Pack.
http://windows.microsoft.com/en-IN/windows/language-packs#lptabs=win7
Regards
Sukrit Dhingra