The Search All Previous Versions (Shadow Files) on All Volumes setting allows you to search Shadow Volumes.
On Windows Vista and later, the operating system provides persistent Shadow Volumes, commonly referred to as Previous Versions and used by the System Restore service. The shadow volumes may contain files, or parts of files, with sensitive information. When enabled, all shadow files across all the drives specified in the Files search will be searched. It is not possible to search only a specific shadow volume or specific path within a shadow volume.
Note: Because shadow volumes are read only, individual shadow files cannot be deleted; however, an entire shadow volume containing a file with sensitive information can be removed using the Shred action.
To view or modify this setting, click the Configuration ribbon, then the Settings button. For additional settings please refer to View and Manage File Types and Options or Settings to Customize Your Experience.