Indexing only first page of a PDF

Indexing a folder of scientific journal articles only result in the first page showing up. I think I manage to get the entire paper being available in DevonThink before. What I am doing wrong?

Indexing normally allows all pages in a PDF to be viewable. However, if your journal has password or other content protection enabled on these documents, viewing might be disabled.

Can you view the entire document in another PDF reader – for example, Preview? If so, you might send a copy to Support for further analysis.