<TextBlock>
    <Hyperlink Click="openFile_Click">Open File</Hyperlink>
</TextBlock>

var appPath = System.AppDomain.CurrentDomain.BaseDirectory;

private void openFile_Click(object sender, RoutedEventArgs e)
{
    System.Diagnostics.Process.Start(appPath + "myFile.txt");
}

<TextBlock>
    <Hyperlink Click="Hyperlink_Click">Click Me..!!</Hyperlink>
</TextBlock>

private void Hyperlink_Click(object sender, RoutedEventArgs e)
{
    System.Diagnostics.Process.Start("filePath");
}

System.Diagnostics.Process.Start("..\..\ABC.txt");

System.Diagnostics.Process.Start("ABC.txt");

<TextBlock>
                      <Hyperlink Command="{Binding CommandPath}" CommandParameter="   {Binding Path=RecordID}">
                    <TextBlock Text="Open File" />
                </Hyperlink>
               </TextBlock>

public ICommand CommandPath { get { return new DelegateCommand(HyperlinkClick); } }


                private void HyperlinkClick()
                  {
                        Process.Start(@"notepad.exe", @"C:TEST_FILE.txt");
                    }