Clue by Clue: The Mystery of Wizard World Solution
Jon Worthington never put the manuscript back in the safe. When everyone went for lunch, he took paper from the printer next to his desk. At the end of the day, he put that paper in the safe and put the manuscript in his bag. Then he made it look like someone had broken in. Jon was tired of writing Wizard World books and wanted to do other projects. Refusing to write them would get him a bad reputation with the publisher. So he stole the copy, hoping the publisher would not insist he recreate the book. Then he could end the series and do more serious projects.
And check out the book it is based on: Clue by Clue by Walton Burns