When Windows System Protection is enabled, Windows periodically creates restore points (snapshots) of the contents of mounted storage drives. Restore points enable files, folders, and system state to be accessed or rewound to an earlier point in time.
If you would like the Merge versions lists (accessed via the Versions 
button) to show the available restore point versions of compared files and folders, check the option Show file and folder versions from System Restore on the Application options page.
Manually created system restore points do not contain the file information required for use with Merge.
Windows System Protection is not enabled on Windows 10 by default. Windows System Protection must therefore be manually enabled if you wish to view older file versions stored for restore points.
To enable Windows System Protection:
- Open the Windows Control Panel.
- Navigate to System and Security▸System▸System Protection.
- Click the Configure… button.
- Select the Turn on system protection radio button.
- Click the OK button.
- Click the OK button.
Windows settings
Each restore point uses an unpredictable amount of disk space, so Windows provides a variety of options to configure whether (and how many) restore points are made. These options can be found under Control Panel▸System and Security▸System▸System Protection. Restore points can be enabled for some or all hard drives, and the space available for use by restore points can be increased or decreased.