I understand that you have to re-orient the XY/min/max to fit a tagRECT but I'm still getting an "Invalid pixel bound value(s)" error. I have also tried setting Ymin/Ymax = bottom/top but I get the same error.

    IMxDocument mxdoc = ArcMap.Application.Document as IMxDocument;
    IActiveView actView = mxdoc.ActiveView;

    IExport exporter = new ExportPDFClass();
    exporter.ExportFileName = @"U:\FILEPATH\topoexport.pdf";
    exporter.Resolution = 300;

    IEnvelope pixBounds = new EnvelopeClass();
    int hdc = exporter.StartExporting();
    pixBounds.XMin = actView.ExportFrame.left;
    pixBounds.XMax = actView.ExportFrame.right;
    pixBounds.YMin = actView.ExportFrame.top;
    pixBounds.YMax = actView.ExportFrame.bottom;
    exporter.PixelBounds = pixBounds;
    tagRECT rectangle = actView.ExportFrame;

    actView.Output(hdc, (int)exporter.Resolution, ref rectangle, null, null);
    exporter.FinishExporting();
    exporter.Cleanup();