I kind of got some solution...
But I am really not satisfied with it. Because the Style of the Preview is not proper.
How can I do a shrink fit to width in style and adapt that style in JavaScript function is my question now...
Can someone help me with that?
function PrintPanel() {
debugger;
var panel = document.getElementById("<%=Upnl1.ClientID %>");
// panel.style.visibility = "visible";
panel.style = 'preview-message';
var printWindow = window.open(panel, '', 'height=600,width=900');
printWindow.document.styleSheets = 'preview-message';
printWindow.document.write('<html><head><title>DIV Contents</title>');
printWindow.document.write('</head><body >');
printWindow.document.write(panel.innerHTML);
printWindow.document.write('</body></html>');
printWindow.document.close();
setTimeout(function () {
printWindow.print();
}, 1000);
return false;
}