In triplicate
Definition 1 of 1
Pro Tip 1/3Official Procedures
Used frequently in formal situations like government or legal documentation where multiple copies are required. 
All contracts must be signed in triplicate for legal processing.
Pro Tip 2/3Exact Copies
Each of the three copies should be identical and complete, not just partial duplicates. 
The agreement was printed in triplicate, with each copy being an exact replica.
Pro Tip 3/3Distribution Purpose
The three copies are often for different recipients, such as one for the sender, one for the receiver, and one for records. 
Submit the expense report in triplicate so finance, HR, and you each have a copy.