I worked on this more, and able to generate the chart and grid from code behind, but the chart is not displayed in the PDF.
The chart does not have a SeriesMapping's but I'm having a ChartArea in which I am adding DataSeries for StackedBar / StackedArea (not at the same time), and finally adding this ChartArea to RadChart. Like this
lobjRadChartDeomposed = new RadChart();
ChartArea lobjRadChartArea = new ChartArea();
lobjRadChartDeomposed.Height = 400;
lobjRadChartDeomposed.Width = 1115;
Adding DataSeries to ChartArea like this:
lobjRadChartArea.DataSeries.Add(lobjDataSeries); // near about 12 series.
Then assigning ChartArea to RadChart like this:
lobjRadChartDeomposed.DefaultView.ChartArea = lobjRadChartArea;
Finally generating the image as mentioned in the help for ExportToPDF for RadCharts.
Find the attachment for the output (copied from PDF)
Please let me know where I'm making mistake, as soon as possible.