If you just want to open the file on a new window, you should use Diagnostics.Process
Like what @Baldric showed, and if you want to save the filename.
string path = "";
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
path = openFileDialog1.FileName;
System.Diagnostics.Process.Start(path);
}
and one more thing I noticed in your code. you want to return the filename but you use
path = sr.ReadToEnd();
is the text in the file contain a path of the file?