how to validate filename and textbox in asp.net using c#

Question

        In run mode as follows
 
        Course Type REO 5 Days(textbox1)
 
       I have one folder in D path. in D drive file as follows
 
       REO 5 Days.htm
 
      I want to validate REO 5 Days textbox1 value and D drive file name REO 5 days must be the same.

      if textbox1 and d drive file name must be the same show the file.
 
      Otherwise show the message filename and textbox name not same.
      for that how can i validate using c#.