Before to study a file, you must import it in the software
If you select a file, you can:
The type of the eventlog is resolved by default with the first and last event. It might be wrong, it is just an indication. (It is the reason of the question mark). It is the reason why you can change it.
The file type decides which sessions could be listed from this file as RAS sessions or print job for the system log. It decides too how to decode the event description. If you choose a wrong type, you could have no description for your events.
You can also have this information with the context menu of the Windows explorer of an evt file, Detail Choice.