Does preCICE use files for the communication?

Communication via files was the norm for quite some time.
Does preCICE use this approach?

No. Using files is very slow and does not scale.

The preCICE participants communicate either through TCP/IP sockets or through MPI ports.

That said, the initial handshake between participants is done via files.
The file system is the only reliable and lightweight method on exchanging initial endpoints.