The commands for what a document carries besides its pages: attachments, metadata and signatures.
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pdfdebug dump embedded [--json] [--ref "N G R" | --name NAME] <file>
Lists attachments and associated files with their name, relationship, MIME
type, size and references. --ref or --name writes one file's raw bytes to
stdout instead; --name fails when no file, or more than one, has that name,
or the one that does has no /EmbeddedFile stream.
pdfdebug dump metadata [--json] [--pretty] <file>
Prints the /Info dictionary fields and the XMP packet.
pdfdebug dump signatures [--json] [--pretty] <file>
Decomposes each signature field: signer, certificate chain and ByteRange coverage. It never says whether a signature is trusted or valid.