I'm not sure if the game is DRM-free or not, but does it need to launch the Steam Client first when you try to play it? If it doesn't then it's DRM-free.
Try to locate the folder it's installed (usually the path is: C:\Program Files\Steam\steamapps\common\[the folder name]), after that you only have to zip all of the files and upload it somewhere, and share the links.
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