ActiveTheme Property
Returns the name of the active theme plus the theme formatting options for the specified document. Returns "none" if the document doesn't have an active theme. Read-only String.
Remarks
For an explanation of the value returned by this property, see the Name argument of the ApplyTheme method. The value returned by this property may not correspond to the theme's display name. To return a theme's display name, use the ActiveThemeDisplayName property.
Example
This example applies a theme and then displays the name of the active theme plus the theme formatting options for the current document.
Sub CheckTheme()
ActiveDocument.ApplyTheme "artsy 100"
MsgBox ActiveDocument.ActiveTheme
End Sub