Drupal Commerce Adding fields to Add To Cart page
Thanks all of you for your valuable time and suggestions. More or less all suggestions 'll be required in near future. I have up-voted all of you for your help. However on other side I got the answer, what I was looking for. 


  It sounds like you need the Customizable Products module.
  
  Once you have that module installed, you can go to Administration > Store > Configuration > Line item types. Add a custom line type and add as many custom fields there as you'd like. You'll see - the
  interface for adding fields to the custom line type is the same as
  when you create a content type, so it's easy to use.
  
  Then, when you've added all the customer info you need in your new line item, go ahead and modify your 'Exam' product to include
  those fields in the product display. Hit the 'Display' settings for
  the content type, and configure the settings for the 'Add to cart'
  field. Make sure you choose the correct line item for it to use and
  Save!
  
  Helpfull screencast could be found at http://vimeo.com/36106455