a) Been AP n Karnataka are different states, you first need to check euro emission norms prevailing in Andhra
If its BS-IV norms in Andhra, then the old car you looking has buy to be BS-IV compliant else it cant be re-registered in your state
b) You need to get NOC issued from Karnataka. Form 27, Form 28 (3 copies) along with Vehicle RC Copy, Insurance, ID and add proof or original owner to be submitted. The NOC issuance then take anywhere from 1-2 weeks
c) Post NOC Recvd, Form 20 with Form 29,30 need to be filled and submitted. This has to be submitted along with Form 28 which you will receive it from original Karnataka RTO. Your id, address proof along with insurance papers will go in with transfer charges, registration charges as applicable including octroi.