You could do this using floating shapes, combined with a MACROBUTTON field coded along the lines of:
{MACROBUTTON ShowHide Text_to_be_clicked}
and a macro like:
Code:
Sub ShowHide()
With ActiveDocument.Shapes(1)
.Visible = Not .Visible
End With
End Sub
where Text_to_be_clicked is the text you want to make clickable.
Note: The field brace pairs (i.e. '{ }') for the above example are created in the document itself, via Ctrl-F9 (Cmd-F9 on a Mac); you can't simply type them or copy & paste them from this message.