AUTOEXEC.DOS is the version of AUTOEXEC.BAT that was used by a stand-alone DOS prior to installation of Windows 95 or Windows Nashville. Both of these allowed to boot the computer in the old version of DOS by pressing F4 during the boot procedure. When doing so .DOS files were moved to their normal position and regular boot files were moved to .WIN extension. Boot loader would restore Windows upon next reboot if .WIN files were present.
This was a dangerous thing to do, since FAT16, used by DOS, did not work with vFAT's long file names, and if one tried to work with long name would be lost. But downgrading was incredibly simple. One simply had to boot to DOS and then delete .WIN files.