It is ok to make a good copy for handwriting identification, but it has no legal effect. Because copies can be compiled. If the copy has the signature or seal of the party concerned, it can be used as legal evidence, but judging from your question, it should be that the original cannot be obtained and there is no signature or seal of the party concerned. Otherwise, you don't need to sign the copy, and you can only obtain evidence in other aspects through the judicial department.