Linking documents: update usage please

Currently you can create a PO from an RFQ, but you cannot create an invoice from either one. You can create a PO from an invoice, but it seems silly to do that when you already have a PO ready from a RFQ. In this situation we should have the ability to manually link a document to other documents. It would seem more logical to be able to create both a PO and an Invoice from the RFQ so all docs are synced and edit where needed.

Right now I have this huge job where I created all these RFQs turned to POs and those POs are useless since I needed to make invoices and create new POs so the docs would link. Again doing work twice which I cannot stand doing! Thanks!