In Asp.Net Server.MapPath method maps the specified relative or virtual path to the corresponding physical path on the server. Server.MapPath takes a path as a parameter and returns the physical location on the hard drive.
Suppose your Text files are located at D:\project\MyProject\Files\TextFiles
If the root project directory is MyProject and the aspx file is located at root then to get the same path use code
/* physical path of TextFiles */