“The last column in the excel template can be dynamic i.e. the data table used for processing can have any one column among Completed Date, Due Date and Reminder Date. So how can this be designed at template level so that if the data table has a Due Date column, the template and the excel should have the respective column"
Well, you can do it, it is very easy. I think first you find out the last column in the data table, and then input the smart markers dynamically into the template file at run time accordingly.
//Find out the last column in the data table
//You code goes here.
//Now You have found that it is DueDate Column
//Get the first worksheet(default sheet) in the workbook.
Aspose.Cells.Worksheet w = workbookDesigner.Workbook.Worksheets;
//Input/change the marker in the cell accordingly.
// Setting Data Source for markers
//Processing the markers.
For further reference, see the document on smart markers: