Well, I had mentioned that it is essentially one page solution.
Anyway, if there are going to be say 20 items, I believe it can be accommodated with a little tweak to the invoice line items table. As we can see, the Articulo values in each row has spilled into 2 lines whereas other columns have very minimal data. I would try to adjust the width (and title ) of the other columns so that the " Articulo" can be accommodated in one line. That will make more items to be accommodated in one page. The columns of Cantidad (can be renamed Qty) , P/U and SUB TOTAL can certainly have much lesser width that will allow the Articulo column to have longer width, thereby accommodating the description in one line.
However, please note that it is essentially one page solution. If with modification, your testing shows that it can accommodate say 20 items, it will not work for 21 items.