Unlike the "Eight Pages" in the park, which are primarily a gameplay mechanic to trigger Slender Man's pursuit, these documents function as that unlock achievements and fill out the Scrapbook menu. They reveal that:
were childhood friends who both shared sightings of the Slender Man. Slender The Arrival
These letters detail the tragic backstory of Kate and her friend C.R., and how the Slender Man influenced them. Key "Deep" Lore Documents Unlike the "Eight Pages" in the park, which
: Tacked to a pole on the playground slide in the backyard. Slender The Arrival