Autoload error: Module 'Magento_Catalog' component already exist

[ZestardTech]

Hello,

I copied {magento root}\vendor\magento\module-catalog 's all directory and files inside  "{magento root}\app\code\Magento\Catalog" directory.

After that i run command php bin/magento setup:upgrade but it will give me following error and also give the same error while access front end and back end :

Error :

Autoload error: Module 'Magento_Theme' from 'D:\wamp\www\magento2\app\code\Magento\Theme' has been already defined in 'D:/wamp/www/magento2/vendor/magento/module-theme'.

Could you help me to understand what's wrong please?

Thank you!

[Rakesh Jesadiya]

You cant override directly Magento Catalog module inside app/code folder, You have to first register your module inside registartion.php file inside your module.

You cant simply override directly in app/code folder  of core module. In magento 2 if you want to overrider any core module you must have to create module with dependency injection. create di.xml file for any php file override of core module.

Thanks.

[ZestardTech]

But,This is already work in magento version 2.0.2 .And then i upgrade it to latest version 2.1.2 and i found this issue. Please help me to solve this.