Any example of doing this? I have Acrobat 5, so can create the PDF.

How do you then use iTextSharp to modify the fields (i.e. do you have any example code)?

Apart from iTextSharp, the tools that generate the PDF's are quite expensive (also, I can only use free components). iTextdotNET uses J#, so I can't use that (but I don't think it offers anything over iTextSharp).