There must be other evidence that can be mutually verified with the copy, and a single copy of evidence cannot be authenticated separately. That is to say, copying evidence should be confirmed by other auxiliary evidence, and evidence chain should be formed between evidences to prove the facts of the case.
There should be justified reasons for the provider of the copy of documentary evidence not to provide the original for verification, that is, there are objective reasons for not providing the original (including reasons that there is evidence to prove that the original copy has been lost and the original is in the hands of others). Subjective reasons cannot be used as a legitimate reason for not providing the original.