Something like that should be what you need
private void button1_Click(object sender, RoutedEventArgs e)
{
// Create OpenFileDialog
Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
// Set filter for file extension and default file extension
dlg.DefaultExt = ".png";
dlg.Filter = "JPEG Files (*.jpeg)|*.jpeg|PNG Files (*.png)|*.png|JPG Files (*.jpg)|*.jpg|GIF Files (*.gif)|*.gif";
// Display OpenFileDialog by calling ShowDialog method
Nullable<bool> result = dlg.ShowDialog();
// Get the selected file name and display in a TextBox
if (result == true)
{
// Open document
string filename = dlg.FileName;
textBox1.Text = filename;
}
}