Write the Text in RichTextBox

private void frmRichTextBoLoad(object sender, EventArgs e)
{
            // write textin RichTextBox
            richTextBox1.Text= "Hello How are you";
}

Change ForeColor of text written in RichTextBox

In RichTextBox each text can be in a different color.

Code:

private void frmRichTextBoLoad(object sender, EventArgs e)
        {
            //Find method is used to find the text written in RichTextBox
            richTextBox1.SelectionStart= richTextBox1.Find("Hello");
            richTextBox1.SelectionColor= Color.Red;
            richTextBox1.SelectionStart= richTextBox1.Find("How are you");
            richTextBox1.SelectionColor= Color.RoyalBlue;
         }

Run the Project

Save RichTextBox Text into File and Restore from File

Code:

Write code in the click event of the button. When you double click on click event then click event handler will create in .cs file.

private void btnSave_Click(object sender, EventArgs e)
{
     //SaveFile Method Saves the contents of the RichTextBox into a file
     richTextBox1.SaveFile("h1.rtf");
}
private void btnLoad_Click(object sender, EventArgs e)
{
  //LoadFile Method Loads the contents of a file into the RichTextBox control
     richTextBox2.LoadFile("h1.rtf");
}

When you click save button then text written in RichTextBox1 will save to the specified file.

When you click the Load button then contents of a specified file Load into the RichTextBox2.