@markstahler - you're right, we wanted to make sure that PDF files could be read after the installation was complete, so we check if Adobe Reader is installed and if it's missing it will attempt to install it. As @Muthoe pointed out, you can always can the Adobe Reader installation.
@pavid - we only install what is necessary to ensure that the game will work
We tried to make the installer as configurable as possible but at the same time, we've tried to make it as simple as possible for the average user, so that they're only a couple of clicks from playing the game.
We'll look into changing the installer, so that it checks if there is some software that handles the PDF file type. Thanks for pointing it out! :)