I want the difference between Master and Document Object in Usertables? and Master Lines and Documents Lines Object in Usertables?.
Besides that, you have to notice that Document Objects uses DocEntry and when your form is associated with an UDO (by ObjectType) it fills the field (if it corrected bounded) by itself.
When Using Master Type, you still have the Code / Name columns limitation.
Hope this helps,
Master usertable is similar in structure to the business partner and item master records in business one. These are generally used when you are using a user defined object functionality. Document object is similar to sales order/invoice, etc... Master Lines represents the child records of the master usertable and document lines represents the child records of the document user table.
Hope this helps