Now I see I would have known that if I'd looked more closely at your screen shot.
I believe the problem is that a PDViewDestination is described as "
contains a reference to a page, a rectangle on that page, and information specifying how to adjust the view to fit the window’s size and shape. It corresponds to a PDF Dest array and can be considered a special form of a PDAction".
A named destination, however, although is can be used with a GoTo action, is not an array as in 32000-1 12.3.2.2, it is a string or name as in 12.3.2.3. So, you cannot coerce the action into a PDViewDestination. It may be that you have to use the Cos layer, plus PDNameTree APIs to look up names.
