Because it's a LiveCycle (XFA) form, there won't be AcroFields but xfa fields. Consider a text field TextField1 in subform MyForm bound to a root data node of form1. To access the value of the field it would be: xfa.form.form1.MyForm.TextField1.rawValue which is a SOM (scripting object model) expression.
That would work from the Acrobat API but I don't think that's proper syntax to access it through iText which I beleive comunicates directly with the pdfs COS Object tree (from what I've been told). If that's the case, I'd use PDFXplorer to helpl you. You'll find the values of fields in datasets under the AcroForm tree.
Again, I'm no expert with iText, so that's as much as I can help you there.
Kyle