Backup and restore
Your data are safe because the Simple Invoice software has function to backup and restore. Select Tools from main menu and next Backup. Default, program will make backup automatically to C\:SimpleInvoice folder. In this mode backup is performed each time after exit program. But you can change it for manually backup when you select Manually and click button. If you want you can change place where backup files should be saved and change default C\:SimpleInvoice path. Example you can select folder on external drive like Drop Box or One Drive. It is even recomended. Backup files are arranged in folders named date like eg. 2017-09-01.
Restore option is very simple, just clik "Select file to restore" button and select file from backup folder. Note that your current data will overwritten and lost.