Ehran wrote the book, that's supposed to be the link to Ehran's past. However, knowing the ego of Ehran the Scribe, he probably plays a key part of the story. At the very least, he is the Dr. Watson, transcribing the events while providing running commentary. He probably doesn't use the name "Ehran the Scribe" but odds are it could be identified as a "relative" of his current identity. And, of course, the handwriting will be the same.

I'd more imagine the story is about a very weak long-lost horror named Asmodus. The horror's magic aura causes spike babies in the area, including at least one troll. It eats children, gives people power in return for sacrifices, creates terror, the whole spiel.

The noble hero Aron arrives in town, recognizes the threat, and recruits the "least useless" citizens to hunt down Asmodus. The troll probably plays a key part of the story. More than likely, Ehran, er Aron, used him as a living body shield while using the available magic to kill the Horror.

Ehran likely described the troll as "twice as tall as a well proportioned being, and four times as broad. Remenesent of a bull, with a leathery hide and horns upon a heavy brow. Boar's tusks extend from the jaw and accentuate the tiny, piggish eyes. He was uneducated, and dull, but not noticeably moreso than any other low-born individual. His one redeeming feature was a willingness to fight.
"He was a throwback to the savage creatures that once wandered the desolate mountains. I (Aron) knew of them well. My noble forebears had conquered the mountains in lost antiquity. They were still spoken of from time to time, along with the other great beasts of the land that had died out; the mammoths and the lions."

The Tome is described as ancient and delicate and should be delivered in as pristine condition as possible. If the PCs start reading/copying it, I would have the first page they open come out in their hand (like old SR books) maybe the next page they turn is so brittle it falls apart as it is turned. If they do not get the hint to leave well enough alone, have some random violence befall them whenever the book gets opened. When they go to get paid, dock it for the book being damaged.

I thought it was stated somewhere that the Baron's theory is wrong and the tome does not verify his theory.

As far as that goes, you could have the tome full of incorrect information so it does not matter if it is read.