Download and install the Epic Games Launcher from www.epicgames.com . Log in with your Epic account (you must have accepted the UE4 license agreement).
To download the full Unreal Engine 4.27 offline installer, follow these steps: download full unreal engine 427 offline installer
The offline installer is a snapshot in time. If you install 4.27 offline, you don't get hotfixes automatically. You are responsible for patching. While 4.27 is stable, you miss out on the seamless integration of new Marketplace plugins that auto-update via the Launcher. You have to manually migrate content, which can sometimes cause version mismatch errors. Download and install the Epic Games Launcher from www