The Goraksha Samhita is a gem for serious practitioners and researchers of Hatha Yoga. While a free PDF may offer a glimpse, (in print or paid e-book) is far more valuable. Avoid low-quality scanned manuscripts from unknown sources; they often contain missing pages, illegible text, or script errors.
“Yoga does not come from a book. But a good book can prevent you from breaking your spine on the way.” – Old Nath saying. goraksha samhita pdf upd