Soundpad stores a working copy of the current sound list every 5 minutes, and once on application exit at %Appdata%\Leppsoft, which is equal to C:\Users\Username\AppData\Roaming\Leppsoft.
Soundpad creates daily backups of the sound list on application start and stores them for one week in the above-mentioned directory. The backup date is stored in the filename in ISO 8601 date format, which is backup-soundlist-year-month-day.spl.
To restore a backup, close Soundpad, delete the working copy called soundlist.spl and rename the backup to soundlist.spl.
After you've saved your sound list or loaded one, you will see the path and name of the list in the title of Soundpad. Whenever you change something in your list, you will see an asterisk in the title, which indicates, that there are unsaved changes.
When you are about to switch computers or re-install the operating system, and want to keep the sound files and sound list, then use the export option: File ▶ Export ▶ Sound files.
Soundpad will ask you to select a directory for the export. All sound files of the current sound list are copied to the target directory along with a new sound list file. Afterwards, you can copy that directory to your new computer and just load the exported sound list file in Soundpad.