Two solutions.
(1) you can call system("notepad.exe srv.txt"); which should do the trick (you may need to add paths into that).
(2) (I think) you can use one of the WinExec functions to invoke srv.txt, which will look up what application is associated with srv.txt and launch it with srv.txt as the first parameter.

system("srv.txt") definitely won't work though. As you correctly observe, system() is for executables only.