This no goood approach, what you are trying to do. Designer is not very capable into handling traditionally made PDFs.
If I were you (and since you wrote that you have simple form needs) I would stick with Acrobat Professional form tools, not LC Designer. Acrobat offers a quite comprehensive set of form tools, which I beleive you will find more than enough.
The difference between these two approaches, is basically architectural. Without me getting into detail, it is actually an AcroForms Vs. XFA approach decision. AcroForms (Acrobat plain vanilla forms) are more suited for tradional PDF forms workflows, whilst Designer forms (which are based on XML) are more suitable when advanced programmatistic controls are needed.
BTW: There is another more suitable forum for LiveCycle Designer. This one is actually for a server side tool, LiveCycle Form Manager.