I just bought a 12.9" iPad Pro. I was surprised to realise that I couldn't read my PDFs in 2 page, side-by-side layout in landscape orientation with iBooks.
Is there any free PDF reader app that provides this feature?
Adobe Reader, Foxit Mobile PDF, & Bookari does that really well.
Adobe has a great looking interface and offers some of the basic necessities you need for PDF viewing. While Foxit Mobile PDF is very technical and straight forward. Foxit Mobile PDF offers more tools than Adobe does for free (Adobe charges for annotation features such as writing on PDFs and other things). Either of the two will work. Bookari is an honorable mention as well).
Readdle Documents has a 2 page view for PDF files and is free.