You can use a RemoteInvokable method to switch pages of a Tiff file by opening the same image at a different frame index.  Something like this:

// Open a particular frame
[RemoteInvokable]
public void Remote_LoadFrame(string url, int frame)
{
   this.WebAnnotationViewer1.OpenUrl(url, frame);
}

The current version of the WebAnnotationViewer(5.0d) does not work inside an UpdatePanel, however, it is possible to use the WebAnnotationViewer along side an UpdatePanel.