John Regan

This plugin adds a simple button to the post editor screen which allows editors to duplicate posts quickly and easily. It’s so simple that no configuration is necessary!
Features
<ul>
<li>Copies with just one click!</li>
<li>Make duplicates from the List or Edit Post view</li>
<li>No configuration needed</li>
<li>Works for all Post Types</li>
<li>Integrates seamlessly with the WordPress UI</li>
<li>Extremely lightweight (~8KB)</li>
<li>Thorough Documentation</li>
</ul>

Simple Copy Post Button

Copies/Duplicates Posts, Pages, and Custom Post Types with just one click.

Priyanka Bhave

This plugin provides functionality to duplicate the post, pages and the CPT’s with all the custom attributes like taxonomies and post meta data.
How to duplicate the posts, pages or CPT’s :
<ol>
<li>Open the posts, page or CPT on click of the menu from the left menu of dashboard.</li>
<li>Click on the duplicate link display in the post title, on hover of the title name.</li>
</ol>

WP Duplicate posts pages & CPT

Duplicate posts, pages and CPT with all custom data.

Simple Copy Post Button vs WP Duplicate posts pages & CPT