How to find path for stream reader to show text file

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C#

ASP.NET

I intend to show a text file from app_data folder.
I get error stating that path could not be found. How to code the correct path?

string inputString;
resultLabel.Text = "";
using (StreamReader streamReader = File.OpenText(@"~\App_Data\New Text Document.txt"))
{
inputString = streamReader.ReadLine();
while (inputString != null)
{
resultLabel.Text += inputString + "<br />";
inputString = streamReader.ReadLine();