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What do you mean by "pkt files"? Any packet capture, or some particular type of packet capture?
Did your lecturer indicate what they modified in the file?
What is the software that's not letting you open the file?
Does it report an error when you try to open the file? If so, what is the error? If not, what happens when you try to open the file?
I would say your lecturer is you first and best source of information.