If you're looking for official sources, Games Workshop's website and their digital store offer various PDF publications, including codex books and novels set within the Warhammer 40,000 universe. For fan-made content, forums like 4plebs or Reddit's r/Warhammer40k can be good places to inquire about specific PDFs or documents.
Please provide more details if there's a specific aspect of the Horus Heresy or a particular PDF you're interested in, and I'll do my best to guide you! horus heresy pdf 4plebs
You're looking for information on the Horus Heresy, specifically a piece related to a PDF from 4plebs. If you're looking for official sources, Games Workshop's