saving form in Reader 4.0

I received an editable PDF form on a computer that had Acrobat Reader 4.0 and was able to save the changes. I bought Acrobat Professional 8.0 thinking that is what I needed to create a form like that. However, even with document rights enabled on the form, a computer that only has Reader 4.0 cannot save the changes. Do I need something additional? Or maybe special licensing rights?
 
Thank you for your help in this matter.