Indicating the file is downloded

Question

Hi:


   Can any one help me how to indicate one  article(PDF) is Downloaded successfully in Asp.Net site.The requirement is  we have a site in which the asp.Net book is published and the PDF copy can be downloaded.One user coming and downloading the PDF, how to express or calculate the PDF file is downloaded once the PDF is successfully downloaded.Can any one give me suggestions or code on this regard.


Thanks in advance