Taking a public document as a copy without due permission amounts to misconduct.
There are two things involved
1)Validity of such document
2)Action for such lifting of the document from a public record for taking a copy without proper permission.
However, when there is larger public interest involved like a fraud on Government with fake documents etc., the authorities may consider that document as evidence and may not proceed against the employee that possessed such a document.
RTI Act provides an authentic way to procure such documents with attestation unless such information is exempted under Sec. 8 (1) (j)
The superior may take this as misconduct and can call explanation from the concerned employee that lifted such document.