Electronic signatures are not all the same. Under European law and the eIDAS Regulation, different types of electronic signatures exist with different levels of legal assurance, security requirements, and technical formats. Choosing the right one depends on who is signing, in which country, what type of document is being signed, and what level of legal certainty is required.
This is one of the questions we hear most frequently from clients at Namirial: “Which type of signature do I actually need for this use case?” The answer requires understanding two distinct dimensions: the legal type of signature (Simple, Advanced, or Qualified), and the technical format in which the signature is applied (PAdES, CAdES, or XAdES).
The Three Types of Electronic Signature under eIDAS
The eIDAS Regulation (EU Regulation No. 910/2014, updated by EU Regulation 2024/1183) defines a hierarchy of three electronic signature types, each offering progressively higher levels of legal assurance and technical requirements.
Simple Electronic Signature (SES)
A simple electronic signature is the most basic form. It includes any data in electronic form attached to or logically associated with other data that is used by the signatory to sign. This covers everything from a typed name at the bottom of an email, to a click-to-agree checkbox, to a scanned image of a handwritten signature pasted into a document.
Simple signatures carry legal weight in many everyday contexts under Article 25 of eIDAS, which establishes that no electronic signature can be denied legal effect solely because it is in electronic form. However, SES offers limited identity verification and no built-in tamper detection. In the event of a dispute, proving that a specific individual made the signature can be very difficult.
Simple signatures are appropriate for internal approvals, low-stakes consents, informational confirmations, and contexts where the parties know each other well and the risk of repudiation is low.
Advanced Electronic Signature (AES)
The Advanced Electronic Signature is the workhorse of the European digital economy. Defined in Article 26 of eIDAS, it must meet four requirements:
- It must be uniquely linked to the signatory — it cannot be attributed to anyone else
- It must be capable of identifying the signatory — proving who signed
- It must be created using data under the signatory’s sole control — so that only they could have created it
- It must be linked to the signed data in such a way that any subsequent alteration of the document is detectable
An advanced signature does not require a physical smart card or token, it can be applied digitally without additional hardware, making it suitable for high-volume remote signing workflows. Methods that can achieve AES include biometric handwritten signature capture, OTP (one-time password) via SMS combined with email delivery, and digital certificates.
Namirial’s electronic signature solutions support advanced signatures based on biometric data and OTP authentication, both fully compliant with eIDAS. Our advanced signature captures over 500 biometric data points (position, velocity, acceleration, pressure of the signing gesture), adds a qualified electronic timestamp, and generates a complete audit trail, providing exceptional evidentiary value in the event of any dispute.
AES is appropriate for the vast majority of commercial contracts: employment agreements, sales contracts, lease agreements, financial products (non-mortgage), NDAs, supplier agreements, and HR documentation. It offers the optimal balance between security, legal certainty, user experience, and cost.
Qualified Electronic Signature (QES)
The Qualified Electronic Signature is the highest level of electronic signature under eIDAS, and is legally equivalent to a handwritten signature in all EU Member States. This means a QES signed in Germany has the same legal force as a wet ink signature in France, Spain, or Poland, with no requirement for local notarisation.
QES has two additional requirements beyond the AES criteria:
- It must be based on a qualified certificate issued by a Qualified Trust Service Provider (QTSP) listed on a national Trust List
- It must be created using a qualified electronic signature creation device (QSCD) — typically a smart card, USB token, or remote qualified signing infrastructure (cloud HSM)
As a certified QTSP, Namirial issues qualified certificates and supports QES creation for organisations operating across Europe. Our solutions include both traditional smart card and USB token approaches and remote qualified signatures, which allow signatories to use a qualified certificate stored in Namirial’s secure HSM infrastructure, eliminating the need to manage physical tokens while maintaining full QES status.
QES is required for notarial acts, land registry transactions, contracts for transfer of real property, certain financial contracts, and public administration procedures that specifically require the legal equivalence of a handwritten signature.
The Three Digital Signature Formats: PAdES, CAdES, XAdES
Beyond the type of signature, the format determines how the signature is technically embedded in or associated with the document. The three main formats used in the European Union are all standardised by ETSI (European Telecommunications Standards Institute).
Understanding the difference between formats is practical, not theoretical, the wrong format choice can mean that signed documents cannot be opened without specialist software, or that multiple signatures cause technical problems.
PAdES: PDF Advanced Electronic Signature
PAdES (PDF Advanced Electronic Signature) is the standard format for signing PDF documents. When a PAdES signature is applied to a PDF, it generates a cryptographic envelope that is itself a PDF file — meaning no special software or reader is needed beyond a standard PDF viewer such as Adobe Acrobat Reader.
Key characteristics of PAdES:
- Universal accessibility: signed PDFs can be opened and verified by anyone with a PDF reader, without specialised software
- Multiple signatures: allows multiple signatures on the same document without invalidating previous ones
- Visible signature: supports a visible graphical representation of the signature alongside the invisible cryptographic signature
- Long-term validation (LTV): PAdES supports embedding of validation data that allows signatures to be verified long after the original certificate has expired — essential for long-term archiving
The main limitation of PAdES is that it only works with PDF files. For other document types, CAdES or XAdES must be used.
PAdES is the recommended format for: communications between individuals, contracts sent to clients and customers, documents that will be shared or archived and need to be verifiable without specialist tools, and any context where the signed document must be immediately viewable by the recipient.
CAdES: CMS Advanced Electronic Signature
CAdES (Cryptographic Message Syntax Advanced Electronic Signature) generates a cryptographic envelope with a .p7m extension after the signature is applied. Unlike PAdES, it can be applied to any file type, Word documents, spreadsheets, images, PDFs, XML files, and more — making it highly versatile.
Key characteristics of CAdES:
- File-type agnostic: works with any document format, not just PDF
- Strong cryptographic guarantee: the envelope wraps the entire file with a robust cryptographic seal
- Counter-signatures: supports counter-signing by multiple parties
- Matryoshka effect for multiple signatures: when multiple CAdES signatures are applied sequentially, each signs the previous envelope, creating nested layers like Russian dolls. This can be managed but requires attention.
- Specialist software required: the .p7m envelope cannot be opened without digital signature software, which limits usability for non-technical recipients
CAdES is the standard choice for inter-company document workflows and professional environments where digital signature software is already deployed across all parties, such as legal firms, public administration, or regulated financial institutions.
XAdES: XML Advanced Electronic Signature
XAdES (XML Advanced Electronic Signature) is the standard for signing documents in XML format, but it can also be applied to images, PDFs, audio files, binary data, and SEPA transactions.
Key characteristics of XAdES:
- XML-native: ideal for data-centric workflows where documents are structured as XML
- Embedded or detached: the signature can either be embedded within the XML file or kept as a separate file associated with the original
- No matryoshka effect: multiple signatures can be applied without nesting envelopes
- B2B and e-invoicing: widely used in business-to-business data exchange, electronic invoicing (Factur-X, UBL, PEPPOL), and public administration workflows
- Automation-friendly: the XML structure is machine-readable, making XAdES well-suited for automated high-volume signing workflows
XAdES is the format of choice for electronic invoicing, supply chain document exchange, public procurement systems, and any workflow where documents are processed primarily by systems rather than read by humans.
Which Signature Type and Format Should You Use?
The right combination of type and format depends on four factors: the document type, the parties involved, the required level of legal assurance, and the processing environment.
For PDF documents shared with individuals or mixed audiences (including clients who may not have specialist software), PAdES is the most accessible and universally compatible format.
For non-PDF files or professional environments where dedicated digital signature software is standard, CAdES offers the most flexibility across file types.
For XML-based workflows, including electronic invoicing, supply chain automation, and public sector transactions, XAdES is the appropriate standard.
In terms of signature type: for the vast majority of commercial contracts and business workflows, Advanced Electronic Signature (AES) provides the optimal combination of security, usability, and cost. For documents requiring the legal equivalence of a handwritten signature, a Qualified Electronic Signature (QES) issued via a QTSP like Namirial is required.
When in doubt about which combination is right for your specific use case, Namirial’s team can provide guidance based on the document type, sector, and jurisdiction involved.
Namirial supports all three signature types and all three formats, allowing organisations to choose the appropriate level for each use case while maintaining full eIDAS compliance across borders. Our platform integrates seamlessly with existing document management systems via API, enabling organisations to embed the right signature type and format into every workflow without requiring any changes to how users work.
