How to make all specific text bold in rchtextbox

To make specific text bold in a RichTextBox control in C#, you can use the SelectionFont property along with the FontStyle enumeration. Here’s an example of how you can achieve that:

private void MakeTextBold(string searchText)
{
    int startIndex = 0;
    
    while (startIndex < richTextBox1.TextLength)
    {
        int index = richTextBox1.Find(searchText, startIndex, RichTextBoxFinds.None);
        
        if (index != -1)
        {
            richTextBox1.Select(index, searchText.Length);
            richTextBox1.SelectionFont = new Font(richTextBox1.Font, FontStyle.Bold);
            
            startIndex = index + searchText.Length;
        }
        else
        {
            break;
        }
    }
}

In this example, the MakeTextBold method takes a searchText parameter, which represents the specific text you want to make bold. The method searches for the searchText within the RichTextBox control using the Find method.

If a match is found, the method selects the text using the Select method and sets the SelectionFont property to a new font with the FontStyle.Bold option.

The startIndex variable keeps track of the position from where the next search should begin. The loop continues until no more matches are found.

To use this method, you can call it and provide the specific text you want to make bold. For example:

MakeTextBold("specific");

This will search for the text “specific” within the RichTextBox control and make it bold.