PDF Association TechConnect 2024 — Virtual: PDF 2.0 Implementor Roundtable
The PDF Association TechConnect 2024 was a virtual developer-focused event bringing together PDF library and tool implementors to discuss real-world PDF 2.0 interoperability, PDF/UA-2 progress, and post-quantum signature preparation.
Official event page →Key takeaways
- PDF 2.0 production implementations had shipped by 2024; page-level metadata consistency and new structure element types were the primary interoperability focus areas.
- PDF/UA-2 validator development was underway — the Matterhorn Protocol was being updated and MathML validation pipeline coordination was in progress.
- NIST published post-quantum cryptography standards in August 2024; PAdES/CAdES updates for PQC algorithms were on the standards agenda.
- Hybrid signatures (classical + post-quantum) were the recommended transition-period approach, requiring both PDF specification updates and HSM firmware support.
- The virtual format proved viable for developer-focused technical sessions, enabling global participation without travel cost.
PDF 2.0 implementor roundtable: interoperability findings
/Aside, /FENote, /Sub, /Em). Creating tools were beginning to emit these elements; consuming tools (validators, assistive technologies) were still catching up. The roundtable mapped which tools supported which structure elements and identified the gaps in the ecosystem.
PDF 2.0 encryption specification ambiguities — The AES-256 encryption implementation in PDF 2.0 had a specific set of requirements that differed from the PDF 1.7 version of AES-256 (PDF 2.0 addressed a known vulnerability in the PDF 1.7 encryption key derivation). Several implementations had implemented the corrected version; some had not updated. The roundtable produced a shared test file set for encryption interoperability testing.
Corrigenda tracking — ISO 32000-2 had received published corrigenda addressing errors in the original 2017 and 2020 editions. Tracking which corrigendum each implementation had incorporated was identified as an ongoing coordination need — implementors wanted a clear tracking mechanism so they could know which version of the specification a given tool's PDF 2.0 implementation targeted.PDF/UA-2 validation: from specification to interoperable implementation
/Aside for sidebar/tangential content, /FENote for footnotes/endnotes) required new validation logic. The question of which content legitimately belongs in an /Aside vs. a /Note was a substantive interpretation question — validators needed to decide what level of semantic checking was appropriate.
MathML embedding validation — PDF/UA-2 allows MathML to be embedded in PDF via /AF (associated files) for accessible mathematical content. Validating that embedded MathML is syntactically valid, that it corresponds to the rendered math formula, and that the structure element referencing it is correctly constructed required coordination between PDF validators and MathML validators. TechConnect 2024 mapped the validation pipeline needed.Post-quantum signatures: preparing the PDF ecosystem
Frequently asked questions
What is the Matterhorn Protocol and how does it relate to PDF/UA validation?
The Matterhorn Protocol is a document published by the PDF Association that breaks down the requirements of PDF/UA (ISO 14289) into specific, numbered, machine-testable checkpoints. PDF/UA is written in normative language suitable for a standards document but ambiguous for automated validation — "content must be in logical reading order" is a requirement that requires interpretation to implement as a test. The Matterhorn Protocol translates each requirement into one or more specific test conditions with clear pass/fail criteria. PDF/UA validators (veraPDF, PAC) implement validation against the Matterhorn Protocol checkpoints. This means different validators are testing the same set of conditions, improving consistency. The Matterhorn Protocol is updated for each new PDF/UA version — Matterhorn Protocol 2.0 covers PDF/UA-2 requirements.
What is a post-quantum cryptographic signature?
A post-quantum cryptographic (PQC) signature uses a mathematical problem that cannot be solved efficiently by a quantum computer, unlike current digital signature algorithms (RSA, ECDSA) which can be broken by sufficiently powerful quantum computers using Shor's algorithm. The NIST-standardised PQC signature algorithms are ML-DSA (CRYSTALS-Dilithium) and SLH-DSA (SPHINCS+). For PDF digital signatures, the transition to PQC means updating the CMS (Cryptographic Message Syntax) signing format that PAdES is built on to support PQC algorithm identifiers, and updating PDF viewers and validation infrastructure. Large-scale quantum computers capable of breaking RSA-2048 are not currently available, but the cryptographic community recommends beginning PQC transitions now for signatures with long-term validity requirements (government archives, legal documents).
What changed in PDF 2.0 encryption compared to PDF 1.7?
PDF 2.0 (ISO 32000-2) corrected a cryptographic vulnerability in PDF 1.7's AES-256 encryption. PDF 1.7 used AES-256 in CBC mode with a specific key derivation process (documented in the PDF Reference) that had a known weakness: the encryption key was derived from the password in a way that allowed certain attacks. PDF 2.0 revised the key derivation to use a stronger process (documented in ISO 32000-2 clause 7.6.4). PDF 2.0 also formally deprecated RC4 encryption (which had been used in PDF 1.x and was still allowed in PDF 1.7) and explicitly removed support for the deprecated algorithms. PDF 2.0 encrypted documents are more secure but are not interoperable with PDF 1.7 readers — older viewers that don't support PDF 2.0 encryption may not be able to decrypt PDF 2.0-encrypted files.
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The PDF tools and standards discussed at this event are available free — no account needed.