Display the file from folder in asp.net using c#

Question

 In D Folder files are stored with the name of course name.
In D folder list of files as follows RM (file)

I have one design page as follows Course name
Dropdownlist (In dropdownlist all course will be displayed)RM(Course)

Then i have one Button Show Button.
When i select the Course (RM). i want to display the RM file content details.

For that how can i do using c#. Display files from folder using c#.