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Copy the managepages directory to your plugins directory and activate the Manage Pages Custom Columns plugin from WordPress. You'll then have access to the manage_pages_custom_column action and manage_pages_columns filter.

Alternatively, you can copy the managepages.php and JSON.php files to your own plugin and distribute them. To use, just include managepages.php using something like require_once('managepages.php') and continue as detailed above. Don't worry about other plugins including the code also, you're protected.