The best way to fetch text files from the server to the client?

Im making an addon and I need to write text files from the client to the server and get the text files from the server to the client. Whats the best way of doing this? Would be easy if I could just call functions that are in the the server script from the client script but I dont think thats possible?

Basic networking via net library.
Why would you use a text files for storing things anyways and not sql databse ?

Im not saving things that would need a database. Think of a advanced duplicator where you can only save files to the server.