veraPDF: open source PDF/A validation through pragmatic
partnership
R. McGuinness

C. Wilson

D. Johnson

Open Preservation Foundation
c/o The British Library, Boston Spa,
Wetherby,
United Kingdom
becky@openpreservation.org

Open Preservation Foundation
c/o The British Library, Boston Spa,
Wetherby
United Kingdom
carl@openpreservation.org

Association for Digital Document
Standards e.V.
PDF Association,
Neue Kantstrasse 14
14057 Berlin, Germany
duff.johnson@pdfa.org

B. Doubrov
Dual Lab spr.
Clos du Parnasse 12C, Brussels,
Belgiumboris.doubrov@duallab.com

ABSTRACT
veraPDF 1 is an open source industry-supported PDF/A
conformance checker developed by the members of the veraPDF
consortium. The software validates all current parts andconformance levels of ISO 19005 (PDF/A[1]). This paper makes
the case for open source format validation and describes the
project’s approach to building and testing the software. It also
explores how the unique partnership between cultural heritageorganisations and PDF industry has created an active open source
community.

KEYWORDS
Validation, conformance checker, open
preservation, file formats, PDF/A, standards

1source,digital

THE PREFORMA CHALLENGE

veraPDF is one of three conformance checkers developed withfunding from the PREFORMA 2 (PREservation FORMAts for
culture information/e-archives) project. PREFORMA’s aim is toempower cultural heritage institutions to gain control over thetechnical properties of preservation files. To achieve this theyissued a call for tender [2], alongside a challenge brief [3] for thedevelopment of open source conformance checkers for document(PDF/A), audio-visual (Matroska, LPCM, FFV1), and image
formats (TIFF). In addition to the delivering software, the three‘suppliers’ i.e. the company or consortium selected to carry out
the work, were directed to “establish a healthy ecosystem aroundan open source ‘reference’ implementation of specific file formats
[3]”.
1
2

http://verapdf.org/
http://www.preforma-project.eu/

veraPDF comprises four components:An implementation checker, which validates all partsand conformance levels of the PDF/A specifications;A policy checker, which allows users to implement
additional custom checks to enforce institutional policy
with respect to the format;



A reporter, which processes the results, producing
reports, both human readable and machine parsable; andA metadata fixer, which repairs metadata in files basedon conformance with the standard.

PREFORMA also requested the development of an integratingshell capable of controlling all the PREFORMA-project
conformance checkers, and potentially others that implement thesame architecture and APIs.
The schedule for the conformance checker suppliers was
divided into three phases:
1. A four month competitive design phase where suppliers
were funded to submit their designs. At this early stage
PREFORMA selected two potential suppliers for eachformat. PREFORMA evaluated the six proposals andchose one supplier for each of the conformancecheckers to develop prototype software.
2.

A twenty month prototyping phase starting in April
2015. Only the three selected suppliers progressed tothis phase, which also prescribed a two month design
review process that took place at the end of 2015.
Following a year of development, the final version 1.0
prototypes were released in December 2016.

3.

A six month testing phase that is ongoing at the time ofwriting. During this phase PREFORMA carries out
acceptance testing of the delivered prototypes.

2.1Open Source for Sustainability

Adoption of open source software for digital preservation in
cultural heritage organisations is high. A survey3 conducted by theOPF (Open Preservation Foundation4) in 2015 showed that 88%
of responding institutions used open source software. Cultural
heritage institutions are increasingly both using and contributing
to the development of open source tools [4].
PREFORMA did not aim to just develop software, they are
just as concerned with establishing active open source
communities around the conformance checker projects. The
project required suppliers to maintain an up-to-date, public sourcecode repository, and upload monthly software releases to
PREFORMA’s open source portal5.
PREFORMA’s intention was to ensure that the source code,
software and documentation remained available beyond thelifetime of the project. This strategy aligns with the OPF’s
approach to sustaining open source digital preservation software
as described in the OPF software maturity model6. The OPF has
experience of both sustaining open source projects including
PLANETS 7 and SCAPE 8 , as well as providing stewardship forstandalone tools such as JHOVE9.
Building on its foundations in both the archival and PDF
software industry communities, the veraPDF consortium has
successfully established a dialog between the PDF industry andcultural heritage organisations through digital preservation andindustry events and webinars, an online and social media
presence, and the open development approach.
2.1.1 Licensing. PREFORMA mandated that eachconformance checker be dual licensed under the GNU General
Public License version 310 or later and the Mozilla Public License
version 2.011 or later. All other project outputs such as test data
sets and documentation were to be licensed under CC-BY-412 The
veraPDF test corpus is licensed and is freely reusable for testing
PDF/A validators.

3

SELECTING FORMATS FOR VALIDATION

Identifying file formats and determining the extent to which
individual files conform to appropriate specifications is an
essential step in many digital preservation workflows. It demands
both detailed understanding of a file’s technical properties, andthe format specification. However, cultural heritage organisations
do not have the resources to employ in-house, specialist

knowledge for every file format which they are obliged topreserve.
According to Artefactual Systems13, developers of open source
digital preservation system Archivematica 14 ; “one of the mostinfluential factors in selecting preservation formats is community
adoption 15 ”. PDF/A was one of the file formats selected by
PREFORMA because the specification is:Complete: final definitive documentation isavailable;
Open and accessible: available to anyone, free ofcharge, or for a one-off nominal fee, so it can bereused without any limitations; andwidely used by cultural heritage institutions andnational archives16.
While there are commercial PDF/A validators available nocomplete or authoritative open source implementations existed.

4

PARTNERING WITH INDUSTRY

The veraPDF consortium brings together a network of
stakeholders with complementary perspectives. Led by the OPF
and the PDF Association 17 , the industry trade group fordevelopers of PDF software, with partners Dual Lab18, DPC19 and
KEEP SOLUTIONS20, the veraPDF consortium combines digitalpreservation and cultural heritage expertise with document
industry backing and comprehensive access to the PDF/A
standardization process.

4.1

The veraPDF Approach

In order to fully understand the format specification, theveraPDF consortium decided to create a test corpus covering allparts and conformance levels of the PDF/A standards. The idea
was that creating test files would highlight any lack ofunderstanding on the veraPDF consortium’s part or reveal
ambiguities in the standards.
When there is a problem interpreting the specification the
veraPDF consortium brings the issue to the PDF Association’s
PDF Validation Technical Working Group (TWG), comprised of
PDF technology experts. It was established to analyse PDF
validation issues in a transparent fashion and also connect
veraPDF to the ISO committee responsible for PDF/A.
The ISO working group responsible for PDF/A (ISO TC171
SC2 WG5) 21 had previously decided that the existing ISO
specifications for archival PDF (PDF/A-1, PDF/A-2 and PDF/A3) would not be revised, even in the light of ambiguities3

http://www.openpreservation.org/documents/public/OPFDigitalPreservationCommun
itySurvey2015.pdf (6.0)
4
http://openpreservation.org
5
http://www.preforma-project.eu/open-source-portal.html
6
http://openpreservation.org/technology/principles/software-maturity/
7
http://www.planets-project.eu/
8
http://scape-project.eu/
9
http://jhove.openpreservation.org/
10
https://www.gnu.org/licenses/gpl-3.0.html
11https://www.mozilla.org/en-US/MPL/2.0/12
https://creativecommons.org/licenses/by/4.0/

13

https://www.artefactual.com/
https://www.archivematica.org/en/
https://blogs.loc.gov/thesignal/2012/10/archivematica-and-the-open-sourcemindset-for-digital-preservation-systems/
16
http://experienceworkshop.preforma-project.eu/wpcontent/uploads/2016/11/20161122_BERT_CHALLENGEBRIEF.pdf
17
http://www.pdfa.org
18
http://www.duallab.com/
19
http://www.dpconline.org/
20
https://www.keep.pt/en
21
https://www.iso.org/committee/337930.html
1415

uncovered by the veraPDF consortium’s project. This isunderstandable as changing a specification undermines any
software developed against the previous version. Instead the PDF
Validation TWG asked WG5 to review the ambiguities uncovered
during the development of veraPDF in the context of thedevelopment of a PDF Association Technical Note. PDF
Association Technical Notes have a good track-record of adoption
by the industry. The development of veraPDF has also directly
influenced the standardisation process, with several issues raisedleading to enhancements in a forthcoming new part for PDF/A. As
such, the PDF Validation TWG was able to influence thedevelopment of next-generation PDF/A specifications.
veraPDF has thus served as a vehicle enabling cultural heritageorganisations to directly influence the standardisation process,benefitting both the digital preservation community and industry.

5 ESTABLISHING GROUND TRUTH
The consortium’s aim when creating test data was to produce acomprehensive ground truth [5] corpus for the PDF/A standards.
veraPDF’s developers carefully examined each clause in thestandards, and developed a formal grammar to describe therequirements in a machine-readable fashion. They then produced
validation rules with an accompanying programmatic test for eachrequirement. PASS and FAIL corpus files were created to test thevalidator’s functionality. Where unable to create a rule, file ortest, or when 3rd party validators were observed to disagree, theissue was raised with the TWG. The process is illustrated in
Figure 1.

Figure 1: veraPDF test corpus development process
The veraPDF test corpus22 comprises over 1,500 PDF files. All
veraPDF development and release software is tested against the
corpus and the results are published online 23 . The veraPDF
developers also test against the existing PDF/A test corpora
produced by the PDF Association:

Isartor PDF/A-1b test suite24

The BFO PDF/A-2 test suite25
In addition to resolving problems interpreting the standards,
the PDF Validation TWG reviewed and approved the final set ofvalidation rules and test files.
OPF and DPC also performed real world testing with theirrespective members. Focusing on reliability, performance andusability rather than validator functionality, this testing provided
valuable feedback for bug fixes and optimisations.
KEEP SOLUTIONS carried out software reviews and tested
external integrations by incorporating veraPDF into RODA 26 ,their digital repository solution.

6 VERAPDF TODAY AND FUTURE PLANS
At the time of writing the veraPDF software is available asversion 1.627. Two distinct implementations are available. Early
prototypes of veraPDF used Apache PDFBox28 as its PDF parser,
and to implement the veraPDF validation model29. Although theveraPDF consortium was aware this was incompatible with
PREFORMA’s licensing requirements the consortium needed aparser, and obtained dispensation to use PDFBox to test its rulebased approach to validation.
Version 0.26 marked the first dual release in which veraPDF
launched its own, purpose-built PDF parser, (the “greenfield”
parser), alongside the PDFBox implementation. The greenfieldversion fully meets the dual licensing requirements with minimal
external dependencies.
As well as enabling cultural heritage organisations to ensure
their files comply to the PDF/A standards, veraPDF also provides
the means to enforce institutional policies. The veraPDF policy
checker allows the user to create their own acceptance criteria(“policy”) using XML Schematron 30 syntax, enablingorganisations to enforce restrictions in line with local policy, but
beyond those stated in the PDF/A standards.

24

https://www.pdfa.org/isartor-test-suite/
https://github.com/bfosupport/pdfa-testsuite
http://www.roda-community.org/
27
http://verapdf.org/2017/06/06/verapdf-1-6-released/28
https://pdfbox.apache.org
29
https://github.com/veraPDF/veraPDF-model-syntax
30
http://schematron.com/
25
26

22
23

https://github.com/veraPDF/veraPDF-corpus
http://tests.verapdf.org/

3

6.1 Policy Example
Many cultural heritage organisations will not accept PDF/A-3
documents because PDF/A-3 allows the attachment of arbitrary
file formats to the archival PDF. This runs contrary to thecommon approach of limiting the number of accepted formats tominimize preservation risk. The veraPDF policy checker can helporganisations identify and analyse files attached to PDF/A-3
documents to ensure they meet acceptance criteria.

6.2

The Future

The middle of 2017 marks a pivotal moment for the veraPDF
project. As PREFORMA’s test phase comes to an end, so does thegovernance and funding they have provided. veraPDF will
become an independent, open source project. The OPF, PDF
Validation TWG and Dual Lab will continue to address issues
raised by users as well as testing and incorporating community
contributions. Beyond this, future development will require
funding.
The veraPDF consortium is developing plans to establish acommunity-led steering group, and explore open source businessmodels 31 such as annual subscription or sponsorship, grantfunding and consultancy for software maintenance and to extend
the software’s functionality.
Unaddressed so far is the fact that PDF/A represents a small
fraction of the document files cultural heritage organisations
ingest; the vast majority are simply PDF (ISO 32000) files.
Developing a conformance checker for the PDF format as awhole is a huge undertaking, requiring many man-years of effort
and resources. However, as the veraPDF validation model isformat-neutral it can be extended to cover all aspects of PDF as
well as PDF subset standards such as the forthcoming PDF/A-next
specification, PDF/X (print), PDF/E (engineering), PDF/UA(universal accessibility), related specifications, and even thirdparty standards.

in building software that meets the needs of the digitalpreservation community and incorporates the specialist expertiseof other sectors.

ACKNOWLEDGMENTS
The funding for this work was awarded to veraPDF by the
PREFORMA project, a Pre-Commercial Procurement32 (PCP) cofunded by the European Commission under its FP7-ICT
Programme under grant agreement no 619568. It runs from 1
January 2014 - 31 December 2017.

REFERENCES[1] ISO 19005-1:2005 Document management -- Electronic document file format
for long-term preservation -- Part 1: Use of PDF 1.4 (PDF/A-1)
https://www.iso.org/standard/38920.html, ISO 19005-2:2011 Document
management -- Electronic document file format for long-term preservation -Part 2: Use of ISO 32000-1 (PDF/A-2) https://www.iso.org/standard/50655.html,
ISO 19005-2:2011 Document management -- Electronic document file format
for long-term preservation -- Part 2: Use of ISO 32000-1 (PDF/A-2)
https://www.iso.org/standard/50655.html[2] Per Elfner. 2007. PREFORMA Invitation to Tender
http://www.digitalmeetsculture.net/wpcontent/uploads/2014/06/PREFORMA_Invitation-to-Tender_v1.0.pdf[3] Bert Lemmens. PREFORMA Challenge Brief.
http://www.digitalmeetsculture.net/wpcontent/uploads/2014/06/PREFORMA_Challenge-Brief_v1.0.pdf[4] Angela Dappert, Rebecca Squire Guenther, Sébastien Peyrard (Eds.) 2016.
Digital Preservation Metadata for Practitioners: Implementing PREMIS. 6.2.25
DOI 10.1007/978-3-319-43763-7.
[5] Nicola Ferro. 2004. Proposal for an Evaluation Framework forCompliance Checkers for Long-term Digital Preservation. In Proceedings of the
12th Italian Research Conference on Digital Libraries (IRCDL 2016). Florence,
Italy.

7 CONCLUSIONS
Cultural heritage organisations cannot be expected to provide
expertise across all the formats they are responsible forpreserving. Active dialog and collaboration with industry sectors
who have relevant specialist expertise [5] is essential to thepreservation of digital heritage, and the veraPDF project has
proven that such collaborations are possible.
Open source software has properties that offer a compellingcase for its use in preservation systems. Source code availability,
publication of quality assurance results and the opportunity toplay a role in developing and testing software can provide
organisations with confidence that is difficult to establish when
dealing with a commercial vendor and proprietary solutions.
The work described in this paper shows that collaborations
between the cultural heritage sector and industry can be effective
31

http://www.digitalmeetsculture.net/wp-content/uploads/2017/03/4.-McLellanBusiness-models.pdf

32

https://ec.europa.eu/digital-single-market/en/pre-commercial-procurement