[galaxy-dev] Choosing between pre-existing file or user-defined file as tool input

Hello, I am building a new tool for Galaxy and I would like for it to have an option for the user to choose his file for input or to use a pre-installed file on the server (in a specific path not defined by the user). Can anyone tell me which is the right parameter type to use in the configuration file? Thank you in advance, Makis Ladoukakis