The System.Diagnostics.Process class's Start method starts the application that the system associates with a file. For example, if the file has a .txt extension, then the system opens it in NotePad, WordPad, or whatever program is associated with .txt files.

Similarly if the file has a .html extension, the system opens it in the default browser. Note that the file can be a URL such as http://www.csharphelper.com or even just www.csharphelper.com.

In this example, when you select a file name from the ComboBox or type one of your own and click Open, the program uses the following code to open the file.

// "Start" the file.
private void btnOpen_Click(object sender, EventArgs e)
{
    System.Diagnostics.Process.Start(cboFile.Text);
}