For convenience, the PDF version of every AOP article is given a temporary pagination, beginning with page 1. This is unrelated to the final pagination in the printed article.
The AOP version is identical to the final online version in every respect regarding content and presentation, except that instead of having a volume/issue/page number it has only the DOI as an identifier.
It can be identified, however, by looking at the footer within the PDF file, which states "Advance Online Publication."
The HTML version of the AOP article will have the AOP logo in the left-hand tool bar.