A "legible copy" refers to a clear and readable version of a document or text. It means that the writing or printing on the copy is neat, easy to understand, and can be read without difficulty. Full definition
(f) An employer who uses an electronic CCF must ensure that the collection site, the primary and split laboratories, and MRO have compatible systems, and that the employee and any other program participants in the testing process will receive a legible copy of the CCF. (transportation.gov)