I agree with those frustrated in this thread. Custom fields allows you only to add static data at the top of the PO form. 

I'm attempting to add 'purchase description' from the itemized product field, which would pull from the product database and be specific per SKU. For my suppliers use, I am listing their internal Unique product code (my SKU and their company SKU don't specifically align) into the purchase description, but its no use if I can't get it to appear on the PO which is what they ultimately receive & process orders from. 

Will have to use excel once again, making the PO functionality in quickbooks redundant/ a waste of time.