Today, “attachments” are a widely used concept in the world of email and text messages. Every email client supports the ability to attach a file; everyone who uses a computer or smartphone learns how to use this feature.
However, attachments in email have many limitations. For example, there is no interoperable way to link an attachment to a certain part of the text in the email body. Nor is it possible to specify in an interoperable way the relationship between the ‘container’ email and its attachment(s). This information - the nature (beyond MIME-type) and purpose of the attachment - can only be described in the email body.
PDF introduced attachments (embedded file streams) in PDF 1.3, in the late 1990s, but this definition only matched the equivalent capability in email.
Associated Files (ISO 32000-2, 14.13) leverage the ubiquity of PDF to build on the commonplace concept of “attachments” in electronic communications with features that email and text-messaging systems cannot match.
First introduced in 2012 with PDF/A-3, Associated Files enhances interoperability by specifying the nature of the relationship between a PDF document and embedded files, as well as (optionally) the object in a container PDF file (e.g. a page, an image, or a structure element) to which an embedded file relates.
The Associated Files model is exceptionally open, and can address a wide variety of use cases. Using the Associated Files feature, PDF writers can provide additional information about files related to a PDF file in a standardized and therefore machine-readable and potentially machine-actionable way. The Associated Files mechanism also provides for connecting metadata about a related object with the related object itself.
With generalized use cases to demonstrate the benefits of this feature, this Application Note provides background to the dictionaries and other entries that define Associated Files in PDF 2.0. As such, it is intended for developers who want to learn about Associated Files in PDF, and how they can improve interoperability of content beyond the exchange of digital paper.
Download PDF 2.0 Application Note 002: Associated Files today!
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