LIBPF does not write any data to disk as individual files.
There is a relational database that stores all information and makes objects persistent. Depending on the underlying RBDMS (Relational Database Management System) this database can actually exist as a single file or as a collection of files.
For example the LIBPF 1.0 demos that you can download from the demos section use Microsoft Access on Windows, and Sqlite on Apple OS X.
On Windows the database file (*.MDB format) can be seen at the location:
C:\ProgramData\Your Profile Name\Application Data\LIBPF 1.0.