FormsCentral can't edit an existing PDF form. That has to be done in Acrobat. Once you have the form in Acrobat, then import into FormsCentral to collect responses.
Does acrobat have all the design functions as form central, like drop down boxes
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It is not exactly the same but you do have most field type available in Acrobat including dropdown fields. Just open the View > Tools > Forms right panel in Acrobat and then click on "Edit" to be able to add/modify fields.