You cannot trigger the access and or manipulation of other non native programs using dosbox, what ever is in your games folder is fair game, but anything out side of dosboxs c: drive is non assessable. Dosbox is just an emulator, unless you mounted dosbox's c drive directly as you'r os's c drive (which is not advised) the only way you can get dosbox to interact with any program is if you put it in dosbox's folder you're not going to be able to manipulate anything other than what is in dosbox's folder using dosbox in any way.
you are right of course but as I wrote you can add much more drives to Dosbox. So if you want to manipulate a file not in your games/dosbox folder (whatever you mount as c), just mount the folder where that file is as d,e,f,g,h,....