1、打开文件路径：      
            OpenFileDialog ofd = new OpenFileDialog();                //new一个方法
            ofd.Filter = "(*.et;*.xls;*.xlsx)|*.et;*.xls;*.xlsx|all|*.*";           //删选、设定文件显示类型
            ofd.ShowDialog();          //显示打开文件的窗口
            string fileName = ofd.FileName;                //获得选择的文件路径
2、打开文件夹路径
            FolderBrowserDialog fbd = new FolderBrowserDialog();
            fbd.ShowDialog();
            folderName = fbd.SelectedPath;                     //获得选择的文件夹路径
3、保存文件
            SaveFileDialog sfd = new SaveFileDialog();
            sfd.Filter = "(*.et;*.xls;*.xlsx)|*.et;*.xls;*.xlsx|all|*.*";           //删选、设定文件显示类型
            sfd.ShowDialog();
            string path = sfd.FileName;

参考： https://www.lmlphp.com/user/57790/article/item/692905/