Now I am running DOpus as a novice I see many built in DOpus viewers already have the ability to zoom pages on the web (though that one is difficult to keep focused, since many websites reject IE and insist on edge), PDF and almost everything else including ability in multipage formats to roll pages same as the system previewer would.
The only extra features using the SumatraPDF plugin appears to provide is search (when available) and show bookmarks (when available) neither of which are always present in the source document.