When this option is chosen by a user, the document will open using default application for that extension type in Windows. You can view, modify, and copy the document there but, unlike using Launch Document, the document will not be saved back to GlobalSearch. If you do not have a default application associated with the specified file type in Windows, and error will be displayed.
Open in Windows is an option enabled by the Launch extension. It will be available in the Document Viewer's Actions menu when a document's file type does not have a corresponding entry in the Launch Table.
Any documents launched using Open in Windows will have temp files stored in C:\Users\<username>\AppData\Local\Temp\Square9\GlobalSearch_Extensions. These files will remain in the temp directory even when the document is closed. Extensions will instead delete all the files within that directory whenever the GlobalSearch Extensions tray application is started.