Published in 2012, PDF/A-3 introduces the concept of "Associated Files" to PDF.
Similar to the concept of an email attachment, associated files are far richer, as they may be associated with not only the PDF itself, but with any element of content in the PDF. Also unlike email attachments, associated files include metadata that can define the semantic relationship between the associated file and the object with which it's associated.
Introducing a new feature by way of a document that otherwise defines a subset of PDF was an aggressive move, but a good one. Associated files hold great promise for implementations that look to enrich the document-sharing capabilities of PDF with machine-readable and many other forms of attachments.
So, of course this feature would go into PDF 2.0! And somehow, the whole ISO TC 171 SC 2 WG 5 committee knew it too, because they saw fit to include the following note in ISO 19005-3, Appendix E.2.:
NOTE 1 These new keys are also defined in ISO 32000-2. As this International Standard is based on ISO 32000-1, it was necessary to copy the material here.
"ISO 32000-2 (PDF 2.0)" also appears in ISO 19005-3's bibliography. As it should, given that it's referenced in the Appendix E note!
Nonetheless, the foresight is impressive, considering that ISO 32000-2 was not published until 2017...
“Reached for comment on this state of affairs, PDF/A’s Project Leader, Adobe Senior Principal Scientist Leonard Rosenthol was categorical: “Hey, at least it turned out to be true!” he said.
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