All AFT Products automatically generate backup files each time you save your model. Backup files will be saved to the same location you have saved your model file to. They will have the exact file name as your model, but rather than having the extension *.fth, *.aro, *.imp, etc., they will have the extension *.001, *.002, *.003, etc.
Every time you click save while working in your model, a new backup file will be created. If the maximum number of backup files already exists, the new backup file will overwrite the oldest backup file. The maximum number of backup files created can be set in the General Preferences window.
In order to use a backup file to open a previous version of your model, simply rename the model file by removing the *.001, *.002 and replacing that extension with the extension of the product you are using (Fathom = *.fth).