There is no known lore about the tomes. Here's some research I did on a related question: Are tomes a part of some quest?
The Mystic Secrets of Tibia are truly mysterious. Most tomes used to spawn in random parts of the map but now don't. Green and grey can only be obtained from fansite contests. The purple, red, and blue can be looted today. You can read more about this Why are tomes a rare item? Now, what I'm about to tell you is all hearsay but it could make sense. But to simply answer your question: Based on my research we don't know if tomes are a part of a quest or ever were.
There's a room in Edron's Hero Cave known as the Star Room or one of the pentagram rooms that you can see in Tibia. However, the Edron Star room is rumored to be what was once the Tome Quest or The Mystic Secrets of Tibia Quest. What is said is that players would place the Tome collection onto one of the tiles and then bam you would get your reward. Some speculate it was a Great Axe or a Silver Mace, which at the time weren't obtainable. However, they say the quest got removed and no longer exists and now the tomes are just decoration or a mystery. Now, there are no pictures or videos to prove this, so this is all speculation! I emailed Cipsoft to see if they could verify if this was a quest removed or not and they advised me:
“Thank you for your message. I understand that you'd like to get some hints. As much as I'd love to help, I can't give you this information due to our policy. There are some "secrets" we don't want to unveil because we think it's more fun and rewarding if you find them out for yourself. However, you might be able to find information about this topic on one of our supported fansites. Or you can ask the community for help on the website forum as well as ingame"
Here's how you get to the Edron Pentagram room which is located in Edron's Hero Cave.
Please note: I tried rearranging the collection in a different order but nothing worked. What I think is maybe each player holds a tome and stands in the corner that corresponds with the tome? The theories go on and on....maybe the room is meant for something entirely else or like mentioned earlier, it's just not a quest anymore or never was.
Also, it could just be a coincidence but when you look through screenshots on Tibia there's a screenshot that says, "Solve the secrets in the mystic ruins of the dark cathedral" Interesting choice of wording, I don't want to mislead anyone, I just think it's adding all the words from tomes into a picture. However, we all know there are quests already in the Dark Cathedral so this could be all misleading but I thought I'd add it. (Source: Tibia: Screenshots)
Tibia Fandom: Pentagram-Shaped Rooms
(not a supported fansite) Tibia Community