Project Zomboid is not a free-to-play game. While Build 39 is an older version of the game (originally released in 2018), it still requires a valid purchase to access legally. Official Ways to Access Build 39

Download: Steam will automatically begin downloading the Build 39 files and replacing your current installation. Build 39 Features & Gameplay Guide

Map Expansion: The game world expanded significantly between Riverside and Rosewood to provide more space for driving and exploration.

Here is everything you need to know about Build 39, why you should avoid "free" downloads, and how to get the game safely. What was Project Zomboid Build 39?