Open-Source Libraries and Tools

Inofficial page on free Factur-X, Order-X and Deliver-X (and XRechnung) libraries and tools.

ZUGFeRD/Factur-X is a standard to embed machine readable XML in electronic invoice PDFs.

Libraries

Ghostscript, in it’s core a C++ library, can be used in a way that it actually produced proper PDF/A-3 Factur-X

Konik GPL Java and C# library for ZUGFeRD 1
Mustang is an APL Java and .net library for ZUGFeRD 1 and 2(=Factur-X) and a command-line tool to extract, combine and validate. It’s open-source REST API has been continued commercially.

Ghostscript can also be used to create PDF/A files from ordinary PDF
iText RUPS can be used, along with a good hex editor to inspect the PDF internal structure, or a Windows-only alternative
MuPDF for windows and linux, mutools show can display simple internal structures
Open source AI/invoice recognition InvoiceNet
Open source OCR/pattern based invoice recognition invoice2data

FNFE uses a odoo plugin which is based on VeraPDF and the CEN Schematron
The ZUGFeRD-community online validation is based on Mustang and embeds VeraPDF and the CEN Schematron as well
Philip Helgers open-sourve-validator Phive can validate almost any invoice XML, including XRechnung, unfortunately not covering PDF-hybrid formats
VeraPDF, validates PDF-A,
Exiftool allows to quickly check PDF/A meta data,

The ZUGFeRD Infopaket includes schema and schematron, example files, specs, codelist and a refererence (called technical appendix)
The CEN Schematron can be used to validate ZUGFeRD/Factur-X XML

The open source accounting application Fakturama
Factur-X extension for LibreOffice is a LibreOffice extension to generate Factur-X invoices from LibreOffice Calc published under the GPL licence (video tutorial)

The XRechnung XSLT can be used to convert ZUGFeRD/Factur-X to HTML
Ultramarin Viewer is a freeware viewer for XRechnung based on these XSLTs, additionally
OpenXRechnungToolbox is an open source cross platform XRechnung viewer as well as
Quba, a open source cross platform multi format viewer (also displaying ZUGFeRD/Factur-X PDF and XML)

Additional data is a python project to support extensions for certain industries like logistics, adding additional information to structured invoices (e.g. the invoice is for kilometres and the additional data contains the amount of miles)
Philip Helger published a java library to convert UN/CEFACT CII to UBL
There is a OpenXRechnungToolbox to visualize and validate XRechnung and Leitweg-IDs
There is an interesting parser for the EN16931 specification documents
xpdf has a interesting pdfdetach command line tool to extract the XML from the PDF