ISDOC: the Czech national standard for electronic invoicing, with a hybrid PDF/XML variant comparable to Factur-X.
ISDOC (Information System Document) is the national standard for electronic invoicing in Czechia. The format is XML-based, open, and is supported by virtually all Czech accounting and ERP software. With the ISDOC.PDF variant, it offers a hybrid format comparable to Factur-X/ZUGFeRD: a visual PDF with embedded machine-readable XML.
An ISDOC document is an XML file containing one electronic document, uniquely identified by a UUID. The format has three representations:
.isdoc-isdoc.pdf.isdocxThe ISDOC.PDF variant works according to the same principle as Factur-X: the recipient can open the invoice as a regular PDF or read the embedded XML for automated processing. The difference is that the embedded XML does not use the CII schema from UN/CEFACT, but the proprietary ISDOC schema.
An informal ISDOC.JSON variant also exists that offers the same data in JSON notation. This makes integration with modern web applications and APIs simpler than via XML.
http://isdoc.cz/namespace/2013ISDOC supports more than just invoices. The schema defines two categories:
Tax documents (root element Invoice, schema isdoc-invoice-6.0.2.xsd):
Non-payment documents (root element CommonDocument, schema isdoc-commondocument-6.0.2.xsd)
The support for advance invoices is a notable difference from EN 16931, where this document type does not natively exist. Czech tax legislation requires specific document flows around advances that differ from the European model.
Although ISDOC.PDF and Factur-X share the same hybrid concept (PDF/A-3 + embedded XML), there are fundamental technical differences:
Read more about the similarities and differences of hybrid invoice formats in Hybrid invoice formats: PDF with embedded XML.
In Czechia, the adoption of ISDOC is closely intertwined with government regulation:
B2G (government): since April 2020, all Czech government institutions must be able to receive electronic invoices. Suppliers to the government submit invoices via the ISDOC system or the Peppol network.
B2B (business): electronic invoicing is not mandatory but is encouraged. Businesses can voluntarily exchange invoices in ISDOC or Peppol BIS format.
Czechia has adopted Peppol, creating a bridge between the national ISDOC format and the European network.
ISDOC was designed as a national standard, which creates a number of challenges for cross-border use.
Conversion required. ISDOC is not natively EN 16931 compliant. For sending via Peppol, an ISDOC invoice must first be converted to UBL. The open-source project isdoc2ubl exists for this purpose, using XSLT transformation.
Information loss during conversion. ISDOC contains Czechia-specific fields, such as the ICO identification number, Data Box references and advance documents, for which no direct equivalent exists in UBL or EN 16931. During conversion, this information is lost or must be placed in free text fields.
Advance invoices. ISDOC natively supports advance invoices (zálohová faktura) and tax advance documents. This document type does not exist in EN 16931. Czech tax legislation requires specific flows around advances that differ from the European approach.
Digital signatures. ISDOC supports embedded XML signatures and timestamps according to its own specification. These are not compatible with the Peppol validation chain.
Fragmentation. The coexistence of three format representations (.isdoc, .isdocx, -isdoc.pdf) complicates interoperability. The .isdocx variant has barely been adopted in practice, which can cause confusion for international partners.
Most Czech accounting and ERP packages support ISDOC, including Pohoda, Helios, ABRA Gen, FlexiBee, Money S3, iDoklad and Fakturoid. Support is also increasing in Slovakia since 2024. Outside these two markets, ISDOC is virtually unknown; international partners expect UBL or CII.
eConnect fully supports ISDOC. Received ISDOC documents are automatically processed and can be transformed to Peppol BIS Billing V3 or other supported formats.
This also applies to the PSB API: ISDOC documents can be submitted directly via the API. The PSB recognises the format, validates it and automatically transforms it to the correct output format for the recipient. This makes it particularly easy for Czech and Slovak software vendors to connect to the Peppol network via eConnect, without having to adjust their existing ISDOC integration.
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