Books app PDF file corrupted and annotations lost

I have been using the Books app on a daily basis to adnotate my books and suddenly when i tried to open one of them, a message popped up saying that "the file is impossible to open". I tried exporting it to files and to pdf reader apps but absolutely none would work because the pdf is corrupted. I have no idea what happened, i don't need the book itself but i made on it so many important adnotations for my exams and the Books app is the only one which had them...