I am working on creation of custom module and it is going to be stuck in a problem where i want to add some predefined data to my custom module while installation, so for that i review pre defined modules and found that there is a file installData.php inside Setup of a custom module

I reviewed module-cms all thing is well set and find out a class included inside vendor\magento\module-cms\Setup\insatallData.php

namespace Magento\Cms\Setup;

use Magento\Cms\Model\Page;
use Magento\Cms\Model\PageFactory;
use Magento\Framework\Module\Setup\Migration;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;

use Magento\Cms\Model\PageFactory;

where to find this PageFactory class, because if i am able to find this then in that manner i am able create a Factory class for my own module.

thanks.