https://msdn.microsoft.com/zh-tw/library/system.windows.forms.clipboard(v=vs.110).aspx

clipboard.cs

private void button1_Click(object sender, System.EventArgs e) {
    // Takes the selected text from a text box and puts it on the clipboard.
    if(textBox1.SelectedText != "")
       Clipboard.SetDataObject(textBox1.SelectedText);
    else
       textBox2.Text = "No text selected in textBox1";
 }

 private void button2_Click(object sender, System.EventArgs e) {
    // Declares an IDataObject to hold the data returned from the clipboard.
    // Retrieves the data from the clipboard.
    IDataObject iData = Clipboard.GetDataObject();

    // Determines whether the data is in a format you can use.
    if(iData.GetDataPresent(DataFormats.Text)) {
       // Yes it is, so display it in a text box.
       textBox2.Text = (String)iData.GetData(DataFormats.Text); 
    }
    else {
       // No it is not.
       textBox2.Text = "Could not retrieve data off the clipboard.";
    }
 }