You can download a Free Demo on Steam that lets you play the first level of the campaign.
The game often goes on sale for as low as $1.99 to $3.99 on platforms like Steam and GOG . doom-2016-pc-game-free-download
A DRM-free version is available on GOG, which allows you to play the single-player campaign offline without a persistent internet connection. You can download a Free Demo on Steam