Rar file not setting password after txt is set inside?

I've set a password on an application using a rar file then I closed the rar file then I tested to see if it will ask for a password so It did, then I dragged a txt readme file inside then I tested it again the file is no more locked why is this. How can the app get locked while the readme file is there, and the user will be able to open the readme file while the app is locked. How is this done on winrar?