Livecycle Workbench is used for creating process and process contains flow of different steps/actions to be performed. For Instance, form is once submitted by user after filling it up, then that form comes as request to second user for his approval via signing etc & so on...If you have this type of requirement then Livecycle Workbench would be the right product. Assuming, PDF Form (XFA) is already or has to be created in Livecycle Designer.