As well as the book this release contains the full game, playable on your PC.
To play Iridis Alpha on Windows, open the command prompt, navigate to the directory containing the file, and run:
.\iatheory_play.pdf
On Linux, run from the terminal as follows:
sudo apt install wine
wine iatheory_play.pdf
The controls are: ctrl to fire, arrow-keys to move.
Of course if you just want to read the book, open it with your preferred PDF viewer!