Pretty self-explanatory there; you are calling a class/method/property which has 2 possible definitions:
1. System.Windows.Documents.Paragraph
2. iTextSharp.text.Paragraph
So the compiler has no clue which one to choose.
Options:
1. Delete the reference (using) from this page of code if you don't need both
2. Define your
Paragraph by its fully-qualified namespace.class.property
iTextSharp.text.Paragraph p = new iTextSharp.text.Paragraph();
System.Windows.Documents.Paragraph p = new System.Windows.Documents.Paragraph();