There are many people that consider Event Horizon to be influenced by and almost act as a prequel to the universe of Warhammer 40K's gothic horror.

Within that universe humanity is able to cross the stars by taking a shortcut through 'The Warp', originally assumed to be an alternate dimension which is actually a Dante-esque nightmare hellscape inhabited by demons and gods.

Were it not for the 'Gellar Field' reality bubble the ships take with them they would quickly be overcome by demons and worse, always looking for a way to crack the material universe and cause havoc.

This is exactly what Sam Neill talks about in the paper scene and exactly what the Event Horizon brought back with it.