To make specific text bold in a RichTextBox control, you can use the following steps in a programming language that supports the RichTextBox control, such as C#:

  1. Set the SelectionFont property of the RichTextBox control to a bold font. This property allows you to modify the formatting of the currently selected text.
richTextBox1.SelectionFont = new Font(richTextBox1.Font, FontStyle.Bold);

Select the text you want to make bold using the Select method of the RichTextBox control. You can specify the starting index and the length of the text to select.

richTextBox1.Select(startIndex, length);

Replace startIndex with the starting index of the text you want to make bold, and length with the length of the text.

  1. Apply the bold formatting to the selected text by calling the SelectionFont property again.
richTextBox1.SelectionFont = new Font(richTextBox1.SelectionFont, FontStyle.Bold);

Here’s an example that demonstrates how to make the word “example” bold in a RichTextBox control:

int startIndex = richTextBox1.Text.IndexOf("example");
int length = "example".Length;

if (startIndex >= 0)
    richTextBox1.Select(startIndex, length);
    richTextBox1.SelectionFont = new Font(richTextBox1.SelectionFont, FontStyle.Bold);

Make sure to replace richTextBox1 with the actual name of your RichTextBox control, and adjust the text and formatting to fit your specific requirements.