@Dochartaigh Got what sorted? I downloaded the exact same games from the exact same site as before and now I have to load them onto retro pie instead of simply cut and pasting into the PC folder?
It IS copy and paste - and after a reboot you'll see all the folders you dropped into the roms/PC folder show-up in the DOSBox/MS-DOS menu item just like Nintendo or SNES or N64 ROMs show up in RetroPie. The only difference is you then have to go into these folders, and click on the DOS executable file (usually a .EXE or .BAT or sometimes a .COM) to launch the DOS game.
EXCEPT when the files you downloaded are installation files instead of the working game files. So just like if you had an old MS-DOS computer, and were using floppy disks, you would have to install the game off the floppies (or CD), to a folder on your hard drive. Then AFTER you do that, you can again reboot and go into the DOSBox/MS-DOS RetroPie menu item and launch the executable file to launch the game.
Another exception is games that use a CD rom along with the installed files on your hard drive. The most common example is probably Warcraft II. It needs files installed to your hard drive, AND a CD-ROM to be able to play the full game. This takes some coding ad you have to setup a little script file to mount the CD in DOSBox.
Also, you might be confusing this process with the RetroPie Ports. On those, I think you can simply drop the files into the directory and it'll just run. Most common examples are Doom, Quake, Duke Nukem 3D, and Wolfenstein 3d. These need to be installed from the optional packages in RetroPie setup BEFORE you drop those files into the correct folder. ScummVM is also another drag and drop platform on RetroPie that plays old DOS games which is very much drag and drop....so you have options.