1st you make purchase order
2 purchase invoice must take directly quantite of purchase order when you put purchase order number or supplier
3 goods receipts must take directly quantity of purchase invoice when you put purchase invoice or supplier
No, because the supplier may not have invoiced the entire order. Or you may have several purchase orders outstanding from the same supplier. If you want to bring everything on a purchase order to a purchase invoice unchanged, use
Copy to... function:
No, for the same reason. But you can also use the
Copy to... function to generate your goods receipt.
Where i can find copy to?
Read the Guide I linked to above. It tells you.