Hi Casandra,
There might be some field named "Open Quantity" at item level.
First, try to add it using Easy Form Editor.
(I just checked it, the item table is bound with Detail Line Items level [or Identified Stock level]. Open Quantity is not there.
The structure is as below.
Delivery Note -> Item -> Material
I am guessing Open Quantity will be at Item level.
)
Second option (the only option) is to add using Adobe Life Cycle Designer.
With ALCD, you can bind a new column with Open Quantity from Item.
Cheers,
Fred