I dont have much idea about "iTEXTSHARP library".But i can suggest one more mwthod so that you get more options to choose.
Step 1:convert data set to xml
We can use DataSet.GetXml() method for that.
Convert that to string(like DataSet.GetXml() .toString())
Write an xslt script to convert the above to pdf format
Use XslCompiledTransform class and its methods Load and transform,to finally convert the xml to pddf.