Edit Image -> Edit Using -> Open With...
The external image editing software I had was installed to a different drive than the C drive. Even though I pointed Adobe to where the EXE was, Adobe just gave an error that it was unable to open the image in the external application. I uninstalled my image editing app, re-installed to the C drive, pointed Adobe to the new path and the image editing app launched and opened the image.

Adobe should not require the external app to be installed to the C drive in order to function.