In Ted Padova‘s post, he said,

Adobe Designer 8 supports two different types of forms: Static forms and Dynamic forms. If a form is created as a static form you can easily convert the form in Acrobat 8 to a PDF form.

and he give the steps on how to convert Adobe Designer forms to Acrobat PDF Forms.

This let me thought that I have also done this kind job before, but I did not rely on Adobe Acrobat, just rely iTextSharp, I have used it in my demo software FormServer, and it also have a online demo, Fill and Save PDF Form online, in fact they are the clone of commercial software.
Here is some features about FormServer,

• support automatically convert static PDF forms created by Adobe Designer to Acrobat Form.
• support save data to PDF Forms without Adobe Acrobat, only Adobe reader is enough.
• support save data to FDF

And a HK company found my FormServer, and asked for the source code of “Converting static PDF forms created by Adobe Designer to Acrobat Form”, finally I sold they on US$400.

PS.
With the examples of Bruno Lowagie,Using iText to Fill PDF Forms Created by Adobe Designer, iText can both support Dynamic Forms and Static Forms created by Adobe Designer now.

There are two example codes focus on how to fill Adobe Designer Forms(XFA Forms, Interactive Forms) with iText written by Bruno Lowagie in answer to questions that were posted to the iText mailing list.
FillDynamicXfa and FillDynamicXfa2
From the java name, we can notice they only support dynamic PDF Forms created by Adobe designer.

btw, I have compiled FillDynamicXfa into native byte code, so they can run without jre installed, and only 1.72M, and will release lately.

P.S.

Adobe LiveCycle Forms
Livecycle forms are XML-based and can be either static or dynamic. They are deployed securely to a user’s browser over any platform and are viewed using Adobe Reader (version 7.0.5 is the minimum version for full functionality). The quality of submitted information is improved through instant data validation and calculations. Captured data can also be transferred directly into an organisation’s core systems, streamlining form-driven business processes as well as improving data accuracy.

More info about XFA from wikipedia

XFA (also known as XFA forms) stands for XML Forms Architecture, a family of XML specifications that was suggested and developed by JetForm to enhance the processing of web forms.
XFA’s main extension to XML are computationally active tags. In addition, all instances created from a given XFA form template keep the specification of data capture, rendering, and manipulation rules from the original. Another major advantage of XFA is that its data format allows compatibility with other systems, and with changes to other technology, applications and technology standards.
According to JetForm’s submission to the World Wide Web Consortium, “XFA addresses the needs of organizations to securely capture, present, move, process, output and print information associated with electronic forms.”[1] The XFA proposal was submitted to the W3C in May 1999.
In 2002, the JetForm Corporation was acquired by Adobe Systems, and the latter introduced XFA forms with PDF 1.5 and the subsequent Acrobat releases (6 and 7) in 2003.[2]
XFA forms are saved internally in PDF files or as .XDP files which can be opened in Adobe’s LiveCycle Designer software.
XFA forms are synonymous with SmartForms in the Australian government.

On RAC, I noticed a bid named “Create a small Interactive & Dynamic PDF Order Form in Adobe Designer”, said

I need a PDF ‘Order Form’ to be sent by email when completed. This form will auto generate a unique serial number, consist of radio buttons, check boxes, javascript validations(scripts), text fields, number fields, etc.
The order form will be used by customners to order personalised products (to have their name on it), the form will have a section for user to enter personalised text, change font, text size, etc.
After filling up the form, the form will have a submit by email button and print button. Submit by email means the form should attach itself in a new email message as PDF and send it to a pre-programmed email address.
The form will be interactive and dynamic which means for e.g. upon clicking a radio button, a section or controls are visible or turned active/inactive – more or less like a software application form!
More details will be given later during bidding.
This interactive and dynamic form will be designed in Adobe Designer however you are free to suggest and (if approved) use any other software to create such a PDF form.

After reviewed the requirement, I think the difficult point is “This form will auto generate a unique serial number”, so I think it would be better if exists a javascript class/function can be used in PDF to create a UUID/GUID, after searching and testing, I found JavaScript UUID Class is what I want.