An LF is a view over one or more PF.
The LF can be created in any library.
What is it you are trying to do?
Have a view over a single file or multiple files?
If it is multiple, your LF you would need to have some value(s) to JOIN the PFs.
You could have multiple formats.
If you need a more detailed answer, please let us know exactly what you are trying to accomplish.