Yes it is possible to make a div or any html element readonly without using JavaScript in
asp.net.
First make add runat="server" attribute and give a id of your element like following code block
<div runat="server" id="myDiv"></div>
Second go to cs file and write this following code.
myDiv.Attributes.Add("readonly", "readonly");
Hope, it'll help you. Let me know, it's worked or not.