This example shows how to make a section of content non-editable. Just add data-block="noneditable" attribute to a tag or wrap some tags with this attribute.
See more how Noneditable blocks work.
<!-- element -->
<textarea id="entry">
...
<div data-block="noneditable">
<h3>...</h3>
<p>...</p>
<p>...</p>
</div>
...
</textarea>
<!-- call -->
<script>
let app = Redactor('#entry');
</script>