//重点为是使用 SelectedRtf  属性        private void button1_Click( object sender, EventArgs e )        {            //mergeRTF为并内容后的 RichTextBox 控件            mergeRTF.SelectionLength = 0;       //不选内容            RichTextBox rtf = new RichTextBox();        //需要合并的RTF            StringBuilder s = new StringBuilder();            //第一个RTF文件            rtf.Text = "C#程序设计";            rtf.SelectAll();            Font f = null;            f = new Font( "宋体", 12 ,FontStyle.Bold);            rtf.SelectionFont = f;      //字体            rtf.SelectionColor = Color.Red;            //加入            mergeRTF.SelectedRtf = rtf.SelectedRtf;            //第二个RTF文件            rtf.Text = "VB.NET程序设计";            rtf.SelectAll();            f = new Font( "楷体", 10, FontStyle.Italic );            rtf.SelectionFont = f;      //字体            rtf.SelectionColor = Color.Gray;            //加入            mergeRTF.SelectedRtf = rtf.SelectedRtf;            //第三个RTF文件            rtf.Text = "美利坚合众国";            rtf.SelectAll();            f = new Font( "黑体", 25, FontStyle.Underline | FontStyle.Bold | FontStyle.Italic );            rtf.SelectionFont = f;      //字体            rtf.SelectionColor = Color.Blue;            //加入            mergeRTF.SelectedRtf = rtf.SelectedRtf;            //第N个            //。。。。        }