PDF Stamps / Barcodes

Hi there. We have a lot of invoices that needs to be authorized by third parties. Some parties have extra demands before they can authorize them. For one of them we are not able to find a solution yet, maybe someone can give us advise.

1. When we receive an invoice we need to add a barcode to the invoice. These barcodes are always unique and numbered in sequence. On the same invoice we need to add a specific code. We have 3 possibilities:  A1000, B2000 or B2000. Is there a way to A) add automatically an unique barcode to the document, first one  for example #10001 second #10002 etc? B) have a option for the same document to add the code easily by a drop down or selecting area. We are looking for a lot of automation. If we have to do it stamp by stamp, printing and with pen would be faster.

I hope I explained it well. Thank you so much! Kind regards, Rick