With T275268 and T192866 metadata for PDF and Djvu files is stored as blobs in External Storage and no longer in the image table. Metadata in the image table just points to the text table, which points to ES content servers.
The issue with this is that now it is not possible anymore to access metadata from the image table SQL dump alone and that text table does not seem to be dumped for Mediawiki Commons. So, I would like to request that content for the PDF/DjVU metadata is dumped. Or maybe there is some other way to provide those blobs.