The "remote machine" is the "server." The machine where the user sits with their web browser is the "client".
An applet's Java code runs on the client machine. Runtime.exec() can only execute applications on the client machine. Perhaps you've gotten this to work (sort-of) in a
test environment where the client and server are the same machine; but in deployment, they'll be separate and this can't possibly work.
To run an executable on the server, you must have code that runs on the server. One possibility is a
servlet. Do you know what those are? The servlet could run the executable, load the text file and send it down to the applet on the client machine.