I seem to have resolved my problem. It was the way I was referring to the fields in my PDF form. I found an article that describes how to do it and the code. Although part of this article says that iTextSharp cannot populate PDF forms created in Adobe
Designer, this code worked for me. I'm guessing that maybe when this post was made iTextSharp may not have been able to do it. I am using 18.104.22.168 and it populates a PDF form generated in Adobe Designer v7.