Depending on how recent it was, I would use the history tool and see if I recognized the source.
It was only within 3 weeks. Could you OR ANYONE show me step by step ASAP? Thanks.
Go to Tools on the Task Bar
Enter History in the Search in the Tools Menu
Select History
Scroll through
Another option is to go to the Library window and sort the display by Last Accessed.
(Click a column heading to sort by it, if the heading is not shown right-click the top of one of the columns and select it from the list)
The history tool could be much improved. It would be great if it was searchable, or could be filtered by time/date/resource/...