II

Poor interoperability prevents File over app software from spreading.

When sharing files over email or messaging apps, we’re effectively limited to a handful of universally supported formats: images, word documents, spreadsheets, presentations, and PDFs. These traditional formats can’t natively handle structured data like machine-readable invoices or digital attestations. When you attach files in newer formats directly to messages, recipients face confusing previews and often don’t know how to open or interact with them.

Some developers have found a clever solution: embedding structured data inside commonly supported file formats. For instance, Inline XBRL embeds financial reports directly into HTML web pages. This works well in some contexts, but email clients block HTML files by default for security reasons, which limits the practical utility of this approach.

Portable documents offer a more promising path. PDF/A-3 (ISO 19005-3:2012) introduced support for embedding arbitrary files as attachments.

A compelling example is Factur-X, which applies this feature to embed EN 16931-compliant machine-readable invoice data within human-readable PDF invoices.

What makes this approach particularly powerful is that the human-readable pages can include instructions for recipients, explaining how to use specialized software to process the embedded data more efficiently.

Portable documents thus provide more than just a technical wrapper for structured data: they offer a standard embedded user interface. Anyone can read the document immediately with common software, while machines can automatically process the embedded data when appropriate software is available.