Roloff‑Matek Maschinenelemente (often styled Roloff/Matek or Roloff‑Matek — Maschinenelemente) is a well‑known German engineering reference on machine elements (bearings, shafts, fasteners, gears, couplings, springs, seals, shafts, fits/tolerances, tribology, strength-of-materials basics, etc.). You appear to be looking for an English PDF or English resources about this book. Below is a concise guide to what the book is, translations/alternatives, how to find legitimate English materials, and recommended substitutes if no official English PDF exists.
While there is of the complete textbook, there are resources and alternatives available for English-speaking engineers. Textbook Overview roloff matek maschinenelemente pdf english