Interactive PDF in Acrobat Merged two A4 portrait pages into one A3 landscape page

After weeks of working on adding elements to create a monster Interactive PDF, it seems the first page and last page are A4 portrait, but I have somehow made all other pages landscape A3 (as in joined together two A4 portrait pages). Somehow all my middle pages have joined - meaning Acrobat is seeing one A3 landscape page rather than two A4 portrait pages. No idea how I have done it or what to do to separate the A3 landscape pages back into two A4 portrait pages. It has interactive elements so preferably a solution that will preserve the elements would be much appreciated.