can i read text file stored on the webserver

I have some code in my default.apsx.cs  file that all works except one very small but important piece..  I have the same code in c# consoleapp and it works fine on my local machine. 
Here is the code...
        // does a datafile already exist
        string stockdatafile = "/"+ stockcode + "_data.csv";
            if (System.IO.File.Exists(stockdatafile) == true)
            {
               
                System.IO.StreamReader objReader;
                objReader = new System.IO.StreamReader ...