If you downloaded the raw PDF from AO3, it is ready for a nice bound book. It will look like a stack of printer paper. To make it look like a real book, you need to "typeset" it.
ATYD is long. If a 500-page book is too daunting, consider the : all the young dudes pdf for printing
However, I cannot produce or distribute copyrighted material, including unauthorized PDFs of fanfiction that may conflict with the original author's wishes or platform terms (e.g., Archive of Our Own’s policy against unauthorized copying/redistribution). Instead, I can offer two helpful alternatives: If you downloaded the raw PDF from AO3,