Javascript/jQuery:
$(document).ready(function () {
$(\'#txt\').bind(\"paste\", function (e) {
var $this = $(this);
$
The jquery event should be:
$('#.txt').on('paste', function() {...});
See example here: Catch paste input
Note the use of a timeout to allow the value to be pasted before you manipulate it.
Once you properly handle the event and get the pasted value, you can add your validation.
Also see ste-fu's answer about referencing the proper field, as asp.net will by default append the container's is to your text box id and the selector '#txt' won't work.