How to replace the values dynamically in pdf doucment using itextsharp through visual studio

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SharePoint2013

I have form for fill the details. That details saved into the share point list. Based
on the list we have generate the document. In the pdf document the content is static. Only change the some values dynamically whenever enter the data into the form.
Here i have generate the pdf using itextsharp. But values not replaced dynamically. How i can replace the values..