1st Step:-
In the start you see designer view change it to classic
2nd Step:-
after that go to file select new file or press Ctrl+n there you see on the right side 4th columb mid Doctype by default is XHTML 1.0 TRANSITIONAL change it to HTML5.
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
</head>
<body>
</body>
</html>
3rd Step:-
after that you see in the last of the same page/window you opened preference tab click it and go to the option default document type (DTD) there is this XHTML 1.0 TRANSITIONA replace it with HTML5 click on OK then click on create you get code like this<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
</head>
<body>
</body>
</html>