Most links to the original PDF are dead links on forgotten forums. If you find a copy, treat it like a rare artifact. It is a reminder of a time when the internet was less centralized and fans were the architects of their own fun.
Since "Liber Xenologis" is not an official Games Workshop publication, but rather a famous (often attributed to the Bell of Lost Souls forums or similar community efforts from the mid-2000s), reviews of the PDF are fascinating time capsules. liber xenologis pdf
Here is an interesting review perspective on the Liber Xenologis PDF, focusing on what makes it a unique piece of Warhammer 40,000 history. Most links to the original PDF are dead
The most interesting aspect of Liber Xenologis is its purpose. It was created during an era where Games Workshop support for Xenos races (anything not Space Marines, Imperial Guard, or Chaos) was abysmal. Since "Liber Xenologis" is not an official Games