February 2013 Update
According to this answer, Adobe Reader XI allows you to save any form of PDF. I tested it myself and it worked.
My old answer:
If you want to generate PDF forms that can be filled out and saved using Adobe Acrobat Reader , you're out of luck. Such PDF files contain an encrypted digital certificate that can only be generated by Adobe Acrobat. Adobe Acrobat Reader checks for this certificate in PDF formats before allowing changes to be saved.
You can then use Adobe Acrobat to create forms, or use alternative methods of obtaining PDF files with filled data inside. One general approach is to include a submit button in your PDF file, which contains the values ββof your fields on the web server, after which you can fill in your PDF file there using the library of your choice.
Here is an example that takes this approach with the Amyuni PDF Creator commercial library.
Editing PDF forms (AcroForms) in a Silverlight application (disclaimer usually applies)
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