Open documents or PDF files on books app ipad

I have 3 pdf files that i have been editing in the books app on my ipad air for 2 years. Last time i checked its size had increased to at least 1gb. Recently these 3 files suddenly could not be opened. I tried everything: using other applications, using different devices, converting it to word and epub, as well as using a pdf repair application, but nothing worked. Anybody have a solution for this?? I really need the file and notes as i have an exam on it tomorrow. Its really stressing me out, please if there are any solutions let me know