Unix server-client files format converter

I need a client-server socket based application where a client uploads a file(from stdin input, full path or the name of the file), then the file is transfered to the server, and the server process that file and converts it to pdf(if it's possible, maybe more format converts, like word, jpg, etc., but it's not mandatory). The converted file should be sent back to the client. The client needs to create an account and login before doing the file conversion. All the accounts should be saved in a text file. The server is written in C(server.c for example) and needs to be multithreaded. Two threads should be for INET regular clients, and 1 thread for a UNIX administrator client. The 2 INET clients are the regular users, which login to an account and then converts a file. 1 client should be written in C(inetclient.c) and 1 in python([login to view URL]), but both of them should do the same thing. The UNIX client will be coded in C(admin.c), and has administrative functions, like adding or deleting an account.