Page.BackPage Property (Visio)
Gets or sets the background page of a page. Read/write.
If a page has no background, its BackPage property returns an empty Variant. Otherwise the returned Variant refers to a Page object, the background page of the indicated page.
To assign a background page to a page, set the page's BackPage property to the name of that background page. To cause a page to have no background page, pass an empty string to the BackPage property.
Markup overlay pages cannot have background pages, so you cannot use the BackPage property to assign a background page to a markup overlay page.
In earlier versions of Visio (through version 4.1), the BackPage property returned an object (as opposed to a Variant of type Object) and it accepted a string (as opposed to a Variant of type String). Because of changes in Automation support tools, the property has been modified so that it accepts and returns a Variant.