A general discussion is provided here and implementation specifics for each methodology are provided in the articles linked below. Each mechanism addresses different workflow needs, but for AcroForms access is limited and indirect.
Fortunately, Acrobat provides some for functionality for Excel for both LiveCycle (XFA) forms and traditional AcroForms. As such, it is very important to be able to move data between Excel spreadsheets and PDF forms.
But it is used like one and Excel is probably the most common local data storage mechanism in use today.
