You do not have to retain the original of any document. These may be retained electronically and are accepted into evidence in Oklahoma and federal courts. The only issue would be if there is a claim that a signature is forged since a handwriting expert not be able to form an opinion as to whether the signature is genuine. but for the vast majority of documents, the risk is minimal. The county clerk where the mortgage is filed can provided a certified copy if needed. On the other hand if you are selling the mortgage to the secondary market, the investor may refuse purchase, so you will need to take that into consideration.