It's alway nice to have an example of readinga textfile. This example also works fine with extra large files > 1 GB.

// open the file; fileLocation can be something like c:\temp\myfile.txt
 using (StreamReader sr = new StreamReader(fileLocation))
{
 // check if there is a new line
         while (sr.Peek() >= 0)
        {
         // read line
                 line = sr.ReadLine();

  // do your thing
  }
}