Generic ebook reader

I have a large number of ebooks in .pdf format stored in iCloud. I have been looking for a generic ebook reader as the Books app won’t import them. I need something that will synch between my iPad and my iPhone, and if possibly my MacBook Air.

I have tried Bluefire and Yomu but both of them have a limit to the number of books that you can have in your library which is less than the number of books that I want to add.

I know I can open them directly from e.g. Finder, but that doesn’t enable me to pick up from where I stopped reading in the same book and at the same place.

I hope that makes sense, and thank you for your advice.