สอบถามเกี่ยวกับการเช็ค type file upload ก่อน submit form ค่ะ

<form action="google.co.th">
<input type="file" id="flFile" /><span id="sFile"></span>
<button type="button" id="btnSubmit">Save</button>
<form>
<script src="jQuery.min.js"></script>
<script>
	$(function(){
		$('#flFile').change(function(){
			var type=$(this).val().substr(-3);
			if(type == 'pdf'){
				$('#sFile').html('<img src="true.png">');
			}else{
				$('#sFile').html('<img src="false.png">');
				alert('File not support !!');
			}
		});	
		$('#btnSubmit').click(function(){
			$('input[type=file]').each(function(index, element) {
                if($(this).val() != ''){
					var type=$(this).val().substr(-3)
					if(type != 'pdf'){
						$(this).focus();
						return false;
					}
				}
            });	
		});
	});
</script>