Hello guys. Let's say i have a richTextBox, which contains text:

DaniWeb is a good IT Forum and I like it.

I want like word 'Forum' to have color red, like:

DaniWeb is a good IT Forum and I like it.

Use MS Word or Windows Wordpad to create a Rich Text File with the formatting that you need.
Open the file in Notepad to see how the formatting is achieved.
Copy the text to the RichTextBox.Text property.

Alternatively, use the RichTextBox methods Find, and Select, to highlight the work and the SelectionColor property to set the new color e.g.

int txtStart = rtb.Find("Forum");
rtb.Select(txtStart, 5);
rtb.SelectionColor = Color.Red;
rtb.Select(0, 0);