Harry would definitely be furious. He's used to fighting against unfairness, and this forced reading would seem like just another form of Umbridge's tyranny. He might try to find ways to disrupt the reading sessions or at least make it clear that he's not going along with it willingly.
In the fanfic, it could have an impact on the relationships between students and teachers. Teachers who oppose Umbridge may secretly encourage students to resist this forced reading. This could strengthen the bond between like - minded students and teachers. On the other hand, students who side with Umbridge may be ostracized by their peers. Also, the forced reading might limit the students' exposure to a diverse range of magical knowledge, as they are stuck with the books Umbridge chooses, rather than exploring a wider variety on their own.
She'd probably be horrified. Fanfiction can have all sorts of wild ideas and interpretations that go against her traditional views. For example, if there are relationships in the fanfiction that she doesn't approve of or characterizations that are different from what she thinks is right, she'll be very unhappy.
She'd be outraged. Umbridge is a very traditional and controlling character. Fanfic doesn't follow the official canon strictly, which would be a big no - no for her.
Hermione might also try to turn the situation around to expose Umbridge's tyranny. She could gather evidence of Umbridge's improper behavior during the punishment process and then use it to convince the other teachers or even the headmaster that Umbridge is a bad influence in the school. This would be in line with her intelligent and problem - solving nature.
Dumbledore, if he finds out, would surely take action. He might not be able to reverse the effects of the Veritaserum immediately, but he would find a way to protect Harry from any long - term consequences. The other members of Dumbledore's Army would be in shock. They would worry about what Harry has revealed and also feel a sense of guilt for not being able to protect him from Umbridge's devious plan. Some of the more rebellious students might even start a protest against Umbridge's use of Veritaserum on a fellow student without proper authorization.
She'd be appalled. Umbridge is all about following the rules and maintaining the status quo. Fanfiction doesn't adhere to the official canon she so firmly believes in.
Some characters might be critical. If they have a strong sense of the 'canon' Superman, they could nitpick at the details in the fanfic that don't match up. For instance, if the fanfic changes Superman's origin story too much, they might frown upon it.
They could be shocked. If the fanfic takes a really unexpected turn, like making a villain into a hero suddenly, the characters might be taken aback. It's like seeing a completely different version of their world.
Some characters might be excited. They could enjoy seeing new adventures created for them in the fanfiction.
They might react with great excitement. The Weasleys are a loving family, and Harry and Ginny are important to them. So they would likely be very happy for the couple and start making plans for their future together.