Existential and intellectual. It arises from the realization that humanity is an insignificant speck in a cosmos ruled by ancient, uncaring, and incomprehensible entities.
The first half of the PDF was a masterclass in the Gothic. It described cathedrals that grew like cancer from the earth, their flying buttresses not supporting weight, but restraining something inside. The text spoke of corridors that breathed, of portraits whose eyes followed not the viewer, but something behind the viewer. the gothic and the eldritch pdf
Given the specificity of the keyword, a single definitive PDF may not exist in the public domain. Here is your action plan: Existential and intellectual