Support PDF attachments (security envelopes)

[Lewis Rosenthal]

Apparently, Poppler provides support for these. Acrobat has the ability to wrap multiple files (PDF and non-PDF) inside a PDF, and optionally password-protect or secure the envelope with a certificate. In addition, each attachment may require a password for decrypting and saving.

It also appears that Poppler can return additional document details (for the info dialog) for such PDFs, including whether there are indeed attachments and what those attachments are.