And how does what you want to do avoid having to manually add an entry to increase the stock hand? There are several possible approaches, but all would entail creating a new records in the ledger table where you enter the quantity into the "Qty_In" field instead of logging stock removal in the Qty_out field.
One method would be to add a Purchase Order table where the related LineItems table is the same line items table used in Invoices. Just keep two match fields in LineItems, one to match to invoices and one to purchase orders. One of the two match fields would be blank in every line item record. You'd use Qty_Out to record quantities sold on the invoices layout and Qty_In to record quantities purchased on the Purchase Order table.
That's just a "concept level" description of what you might do. There are additional details to manage here as you probably would not want to count your ordered products as part of inventory until the shipment is received so you typically need to have some ability to "check off" ordered items as received once the order is received and that change to a field in the line items layout can control when the ordered quantity can now be included in the "on hand" totals.
There are simple as well as fairly complex ways to manage this depending on the needs and operational details of your business.