We are using Adobe Reader 8. We have someone who has scanned in a mix of A4 and A3 size pages to create a single PDF document. They now need to be able to determine what the original size of the scanned pages were. Can this be reliably done by right clicking on the page - going to Document Properties - clicking on the Description tab - and using Page Size as an indicator as to the original scanned page size?
No. This refers to a single document size not a page size. The page size differs. You can try to view the size with the ruler.