I know, I'm not english native. First you say you have to burn a bootable .iso and want to add an additional file, now you came with a .rar.
What I see in the picture is not an OS instalation disc and even it is in an .iso that you see and think it is a .rar, because you let WinRAR to associate and open .iso files, you can't make it bootable.
So, if you have a real OS instalation disc as bootable .iso and want a .text file in it that eventualy will work as it should, you know by now what to do.
If it's realy a .rar just extract to a temp directory, add what you want and use Build mode.
Thanx. This is solved for me then. Thank You