DESPERATE NEED OF HELP: "the document cannot be opened because it is corrupted or damaged"

I was reading this pdf book for weeks now. I have been highlighting a lot of important details and noting down on it since. I'm using mainly my iPad to access it using Adobe Acrobat application.

Earlier today, the app logged me out of my account for no reason. When I logged back in, I can no longer access the file. It says: "the document cannot be opened because it is corrupted or damaged"

Tried accessing it on my Android, same error message. On my Acrobat on my PC, same problem. On my browser, same.

How can I fix it? I tried some online pdf recovery websites, but no help from them.

If there's no way to fix it, what app ASIDE FROM ADOBE APPS can I use to do the same tasks without risking my documents to become corrupted?