If you are a student: Check your university's Springer or O'Reilly portal. 70% of universities have a site license that gives you exclusive, legal access to the full Red Book library.

Be cautious of websites claiming to offer a "10th Edition PDF exclusive" or "Updated" 10th edition files; these are often misleading or potentially harmful files as no such edition exists in the official series. The OpenGL Programming Guide

The Official Guide to Learning OpenGL, Version 4.5 with SPIR-V