Use ToolStrip Control from ToolBar.It provides the Button with Check and Uncheck facility.
Make CheckOnClick Property True for that buttons.
Use following code :
If ToolStripBoldButton.Checked Then
txtNotePad.SelectionFont = SetTextBold
Else
txtNotePad.SelectionFont = SetTextRegular
End If
Similarly you can use following code :
txtNotePad.SelectionFont = SetTextRegular
txtNotePad.SelectionFont = SetTextItalic
txtNotePad.SelectionFont = SetTextUnderline
I hope it will help you :)