How can I insert a Print button that prints a form in a webpage

Print the whole page

Try adding a button that calls window.print()

<input type="button" value="Print this page" onClick="window.print()">

Print a specific portion/container in a page

<div id="print-content">
 <form>

  <input type="button" onclick="printDiv('print-content')" value="print a div!"/>
</form>
</div>

then in the HTML file, add this script code

<script type="text/javascript">
    function printDiv(divName) {
        var printContents = document.getElementById(divName).innerHTML;
        w=window.open();
        w.document.write(printContents);
        w.print();
        w.close();
    }
</script>

Refer Print <div id=”printarea”></div> only?