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

Print 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 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();
}

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