How to add custom fields to Invoice PDF?

Hi all, I am new to Magento. I was tasked to add 2 fields concerning customer’s company. I’ve added them in customer attributes and they show up on registration form but also I need to display data from those fields in Invoice pdf. What’s the easiest way to accomplish this? I assume some extension would come handy but I am not sure which one. If someone would suggest some of them that could accomplish just that, it would be greatly appreciated.