Hi,
That depends. A good IT department should have some kind of audit trail in place. They might be able to track and determine who created the file in question, who has accessed it, and under which user account(s) or from which workstation(s).
It would not be wise to delete or edit the file yourself, especially if it is audited, as your actions may be deemed suspicious.
Depending on the severity and nature of this issue, and your moral obligation, you might consider confronting and talking to the co-worker who created the file (if you know who it is) to try and resolve the issue yourself if it's only a relatively small matter. Otherwise, if it is a more serious and sensitive matter, it would probably be best to raise the issue with a superior, and let them deal with it.