Rich Text Editor can be configured via readOnly property thats defines whether RichTextEditor should be an active HTML editor, or a read-only document viewer.
Hello world!

<p>
<button class="btn btn-primary btn-wide transition-3d-hover mb-4 mb-sm-0 mr-3" onclick="toggle_readOnly()">Toggle ReadOnly</button>
</p>
<link rel="stylesheet" href="/richtexteditor/rte_theme_default.css" />
<script type="text/javascript" src="/richtexteditor/rte.js"></script>
<script type="text/javascript" src='/richtexteditor/plugins/all_plugins.js'></script>
<div id="div_editor1">
<p>Hello world!</p>
<p><img src='/images/editor-image.png' /></p>
</div>
<script>
var editor1 = new RichTextEditor("#div_editor1");
function toggle_readOnly() {
if (editor1.getReadOnly())
editor1.setReadOnly(false);
else
editor1.setReadOnly(true);
}
</script>