操作cad 内存,修改CAD在内存中的打印纸张参数，怎么操作？

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                Assembly asm = Assembly.LoadFile(@"D:\vsproject\CadBatch\CadBatch\libry\acdbmgd.dll");
                Type t1 = asm.GetType("AcDbPlotSettings");

                object oPubClass = Activator.CreateInstance(t1, new object[] { theLayout.ModelType });


                MethodInfo oMethod = t1.GetMethod("getPlotPaperSize", BindingFlags.Instance | BindingFlags.NonPublic);
                Point2d pntop = default(Point2d);
                object result = oMethod.Invoke(oPubClass, new Object[] {&pntop.X, & pntop.Y });
                Type object21 = result.GetType();
                Object object22 = Marshal.PtrToStructure(plotSet.UnmanagedObject, asm.GetType("AcDbPlotSettings"));