SaveFileDialog sfd = new SaveFileDialog();
string stringCon = @"Data Source=(LocalDB)v11.0;AttachDbFilename=|DataDirectory|BakodahDB.mdf;Integrated Security=True";

if (sfd.ShowDialog() == DialogResult.OK)
{
    using (SqlConnection conn = new SqlConnection(stringCon))
    {
        string backupStmt = string.Format("backup database [" + System.Windows.Forms.Application.StartupPath + "\BakodahDB.mdf] to disk='{0}' WITH INIT ", sfd.FileName);

        using (SqlCommand sqlComm = new SqlCommand(backupStmt, conn))
        {
            conn.Open();
            sqlComm.ExecuteNonQuery();
            conn.Close();
        }
    }
}