I think you are clear about the subcontracting from your side along with Annexure 4. What you need is how to bring material into stock. One option is to maintain this material as non-valuated(UNBW) and do Goods Receipt in 501 movement type. Another option is to configure "auto PO" during GR so that PO is created automatically for each GR.
As per my knowledge,i dont think SAP has anything called Annexure 3. You can develop your own form for that. Anyway can you attach the scanned copy.
Regards
Binoy