Drag and drop RichTextBox control from the toolbox on the window Form.

Write the Text in RichTextBox

Code:

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)  Handles MyBase.Load
  
        'Find method is used to find the text written in RichTextBox 
        RichTextBox1.SelectionStart = RichTextBox1.Find("Hello")
        RichTextBox1.SelectionColor = Color.BlueViolet
        RichTextBox1.SelectionStart = RichTextBox1.Find("How are you")
        RichTextBox1.SelectionColor = Color.DarkOliveGreen
  
    End Sub
End Class

Run the Project

Save RichTextBox Text in File

Code:

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       ' SaveFile Method Saves the contents of the RichTextBox to a file.
         RichTextBox1.SaveFile("hello.rtf") 
     End Sub
     Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)  Handles Button2.Click
  'LoadFile Method Loads the contents of a file into the RichTextBox control.
         RichTextBox2.LoadFile("hello.rtf")
    End Sub

Run the Project

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

When you click Load button then saved file will load in RichTextBox2