How to stamp Date-Time on all the pages in an application when requested?

Use the global.asax file and listen to the PostRequestHandlerExecute event of the Global object. In the handler Global_PostRequestHandlerExecute write the following code

VB.NET

Response.Write("This page is updated on " & DateTime.Now.ToString())

C#

Response.Write("This page is updated on " + DateTime.Now.ToString());