It depends on what you want. According to iText documentation, iText supports such
interactive element as AcroForms.
These functionality of such elements are described here:
http://en.wikipedia.org/wiki/Portable_Document_Format#Interactive_elements[
^].
As to iTestSharp, its releases are synchronized with iText, so the same features should be available. For most of the documentation, you need to look at Java documentation, which is easy to understand for a C# developer.
A "fillable field" is represented by the class
com.itextpdf.text.pdf.TextField
:
http://api.itextpdf.com/itext/com/itextpdf/text/pdf/TextField.html[
^].
This is some basic C# code sample:
http://kuujinbo.info/iTextInAction2Ed/index.aspx?ch=Chapter08&ex=TextFields[
^].
You can look for the questions on interactive PDF elements in this forum:
http://support.itextpdf.com/forum/17[
^].
—SA