I am dealing with a Flash file which has been created by a third party. It has a lot of folders and files in the library and I can\'t seem to find any ActionScript anywhere.
You can try the Movie Explorer, Window -> Movie Explorer, or ALT + F3 in Windows. This lets you explore all assets that are added to the stage in a tree like fashion. It wont show items that are dynamically added from the library, but it might be a good starting point.