I think common sense would be to put the *.ADF file in the same location as all the other *.ADF files.
First determine the size of the hdd. Also you need to know if it is in fact running Dos/Windows. It could well be running OS/2. Making a backup of the design program of floppy should be a trivial exercise unless there's some weird protection scheme.
Backing up a 100meg plus hard drive to 1.44 disks isn't fun. A better option may be a parallel port zip drive. Another option is can do a parallel port file transfer to another using a file transfer program. modem7 has a copy of Laplink for dos on his site IIRC. Depending on the version of Dos there my also be tools already on the system you can use. Of course you can also aquire a MCA nic(with the correct *ADF of course) and transfer files that way. That's probably a better long term option. Look up mTCP(created by a member here) on this site and google. You can use use the FTP suite to transfer files to a more modern box for safe keeping. Another option with a nic is use MS Dos network client and NETBEUI to transfer files to an XP box(with the NETBEUI protocol installed obviously)
http://support.microsoft.com/kb/301041