Finding an app to sign documents is easy. Finding one that delivers real legal validity, complete traceability and an experience that does not slow down your workflow is a different matter.
Not all signing applications are equivalent. Some generate a stroke image over a PDF with no cryptographic guarantee; others produce advanced or qualified electronic signatures backed by trust providers regulated under eIDAS and Law 6/2020.
This guide explains what separates one from the other, which signature level each type of document requires and how Legalpin, an encrypted certified digital messaging platform that turns every electronic communication into legal evidence, integrates electronic signature within a certified notification flow that closes the complete evidence chain.
What a document signing app actually does
An electronic signature application allows one or several people to link their identity to a digital document in a way that records who signed, what they accepted and when they did so.
The technical mechanism varies by level: it can be as simple as a signature link with an OTP sent by SMS or as robust as a qualified certificate stored on a hardware device recognised by the European trust list.
What all serious solutions have in common is that the signed document cannot be altered without invalidating the signature, and that a verifiable record exists that can be presented as evidence in litigation or before a public authority.
What an electronically signed document with legal validity is not
A common mistake is confusing the appearance of a signature with a signature with real probative value.
Inserting a JPG image of your handwriting into a PDF is not an electronic signature: there is no cryptographic link between the image and the document, and anyone can copy that image into another file.
Using the built-in signature tool in Adobe Acrobat without a valid personal certificate issued by a recognised authority does not produce an advanced or qualified signature either: it generates only a visual mark with no integrity or signer identity guarantees.
For a signature to carry robust legal weight, the application must work with valid digital certificates, signer authentication mechanisms and a time stamp certifying the exact moment of signing.
The signature levels a professional app must support
Under the eIDAS Regulation, there are three levels of electronic signature with different requirements and different guarantees.
A professional application must let the user choose the right level for each document type, not force them to always use the minimum for ease of implementation.
Simple signature: for low-risk acts
The simple signature identifies the signer in a basic way: it can be a name in a text field, an email confirmation or a checkbox on a platform.
It works for acceptance of terms and conditions, internal read confirmations, named surveys or authorisations of low legal relevance where context provides sufficient evidence.
It is not suitable for commercial contracts, employment communications with legal consequences or any act where the other party could deny having signed.
Advanced signature: the standard for most businesses
The advanced signature meets the four requirements of eIDAS Article 26: uniquely linked to the signer, capable of identifying them, created using data under their sole control and able to detect any subsequent alteration of the document.
In practice, the best applications implement it via OTP to the signer’s phone number, a software personal certificate or stroke biometrics with graphometry. The signer does not need to install anything: they receive a link, verify their identity and sign in seconds.
This is the ideal level for the vast majority of employment contracts, commercial agreements, NDAs, purchase orders, financial authorisations and communications with legal effects.
Qualified signature: for acts requiring maximum guarantee
The qualified signature requires the signer to hold a qualified certificate issued by a Qualified Trust Service Provider (QTSP) and to use it from a qualified signature creation device (QSCD).
Its legal effect is equivalent to a handwritten signature across the entire EU (Art. 25.2 eIDAS), with no possibility of formal rejection. It is required for acts before public authorities, certain remote notarial procedures, mortgage contracts and some tax forms.
A serious application must offer this option or integrate with the QTSPs that provide it.
What a professional document signing app must include
Not all features of a signing application are equally important. These are the ones that determine whether the tool is fit for business use or only works for simple cases.
Robust signer authentication
The application must verify who is signing before recording the signature. The most common mechanisms are OTP by SMS or email, identity verification by video or document, personal digital certificate or stroke biometrics.
Without robust authentication, the signature can be repudiated: anyone who accesses the link could sign on behalf of another person without leaving a distinguishing trace.
Integrated time stamping
Every signature must be accompanied by a qualified time stamp certifying the exact moment at which it was made.
Without it, one of the parties can claim the document was signed on a different date to the real one, which can have serious consequences for contracts with deadlines, employment communications with retroactive effects or administrative acts with cut-off dates.
Downloadable and verifiable record
The application must generate a downloadable signature record: signed document, signature certificate, activity log (who opened the link, when, from which IP or device) and time stamp.
This record must be independently verifiable without needing to access the platform that generated it, using standard validation tools such as the EU electronic signature validator.
API integration
For companies with volume, signing cannot be a manual one-by-one process. The application must offer a documented API that allows signature requests to be launched, statuses to be checked and records to be archived from the company’s CRM, ERP or document management system.
Multi-channel coverage: email, SMS and web access
Signers are not always in front of a computer. A good signing application sends the request by email and SMS, offers optimised mobile access and does not require the signer to install any application on their device.
Use cases by professional profile
Lawyers and law firms
Law firms need to sign client contracts, fee agreements, powers of representation and communications with procedural value. The advanced signature covers most acts; for those requiring a qualified signature, the application must integrate with the authorised QTSPs.
Legalpin’s electronic signature also allows the signature to be linked to the certified email or buromail, so the record includes both certified signer identity and certified document delivery.
Human Resources
HR signs in volume: employment contracts, addenda, disciplinary communications, dismissal notices, non-disclosure agreements and working hours amendments. Each of these documents can have legal consequences in employment disputes.
Electronic signature with integrated certified notification guarantees that the employee not only signed, but received the document at the date recorded in the file.
Management agencies and property administrators
Management agencies handling documents for dozens or hundreds of clients need an application that allows multiple signature requests to be launched in parallel, each one tracked and automatically archived once signed.
Finance departments
SEPA mandates, debit authorisations, financing contracts and payment deferral agreements are documents that must be signed with complete traceability. Legalpin’s certified invoice combines signature and delivery proof in a single record.
Freelancers and small businesses
A freelancer signing contracts with clients or suppliers needs a simple application without unlimited per-user licences or complex technical infrastructure. Access through the Legalpin portal or a basic API integration covers this profile with the same level of legal certainty as a large enterprise.
Signing from mobile: what changes and what does not
More and more signers receive the request on their phone and sign from there. This is perfectly valid if the application is optimised for it.
What does not change is the level of legal certainty: an advanced signature made from a mobile with OTP is just as valid as the same signature made from a desktop computer.
What does change is the signer experience: the application must adapt to the screen format, offer comfortable document reading before signing and send the signature request to SMS or email with a direct access link that requires no installation.
Applications that require installing a native app have lower conversion rates: many signers abandon the process before completing it if they are asked to download something. The best solutions work entirely from the mobile browser.
Differences between signing a generic PDF and using a certified platform
A popular PDF editor may allow you to “add a signature” to a document, but this is not equivalent to an electronically signed document with robust legal value.
The fundamental difference lies in who certifies the signer’s identity and who guarantees the document’s integrity over time.
With a certified platform like Legalpin:
- The signer’s identity is verified via OTP, certificate or biometrics before the signature is recorded.
- The stamped document receives a cryptographic hash that detects any subsequent alteration.
- The time stamp certifies the exact moment of signing.
- The complete record (document, certificate, log, stamp) is downloadable and independently verifiable.
- The signature is issued under PAdES, XAdES or CAdES standards recognised by eIDAS.
With a generic PDF edited visually:
- There is only a visual image or mark with no cryptographic link.
- There is no signer identity verification.
- There is no qualified time stamp.
- The document can be modified afterwards without detection.
- There is no externally verifiable record.
How to integrate a signing app into your business processes
Technical integration does not need to be complex. Most business cases are solved with one of these three approaches.
Direct portal access: the team accesses the Legalpin platform from the browser, uploads the document, enters the signer’s details and launches the request. This is the fastest option for low volumes or teams without internal technical support.
API integration: the Legalpin API allows the signature flow to be fully automated: the internal system generates the document, sends it to Legalpin via API, Legalpin notifies the signer, records the signature and returns the complete record to the originating system without manual intervention.
Third-party platform connectors: for companies already using specific CRM, ERP or document management tools, integration can be achieved via connectors or webhooks that synchronise the status of each signature in real time.
The complete cycle: certified notification plus signature
Signing a document without certified proof that it reached the signer leaves an evidential gap the other party can exploit.
The flow we recommend at Legalpin combines:
- Sending the document via certified email or buromail with delivery receipt and time stamp.
- Requesting the signature on the same document, with OTP or certificate authentication.
- Archiving the record with all elements: hash, stamp, receipt and signature certificate.
- Optionally, certified SMS as a parallel reminder if the signer has not acted within the expected timeframe.
This unified record closes any possibility of challenging the signing process.
Mistakes that invalidate or weaken an electronic signature
Signing a version that is not the final one. If the document is modified after signing, the signature is invalidated. The correct flow requires the document to be in its final version before starting the signing process.
Failing to keep the complete record. Losing the signature certificate, the activity log or the time stamp weakens the evidence chain even if the signed document is intact.
Sending the signature link to the company’s generic email address. If the signature link arrives in a shared inbox, it is not proven that the person who should have signed received and read it. It is preferable to send it to the signer’s named personal email or mobile phone.
Not verifying the signer has authority to bind their company. The advanced signature proves that person signed, but not that they had authority to bind the entity. For contracts with legal persons, verifying the power of representation remains necessary.
Using a non-eIDAS-certified application for acts that require it. Many signing applications on the market do not comply with eIDAS standards for advanced or qualified signatures: they generate a visual mark without certified cryptographic backing. Before choosing a tool, verify it is backed by a QTSP on the EU trust list.
Sign documents with legal certainty
- Advanced electronic signatures compliant with eIDAS
- Authentication, time stamping and verifiable evidence record
- Certified delivery by email, buromail or SMS
Frequently asked questions
Do I need to install anything on my computer or the signer’s device?
With Legalpin, no. The entire process works from the browser, both for the person sending the signature request and for the person signing. The signer receives a link by email or SMS, accesses it from any device and completes the signature without downloading anything.
Can I sign PDF, Word or other format documents?
Yes, although the professional standard is PAdES-signed PDF (PDF Advanced Electronic Signatures), which is the format recognised by eIDAS for electronic signatures in PDF documents. Other formats can be converted to PDF before the signing process.
What if the signer does not have a digital certificate?
Advanced signature via OTP does not require the signer to have a digital certificate installed. They only need access to their verified phone number or email address to authenticate and complete the signature.
How long does an electronic signature take to complete?
In a well-designed flow, the signer receives the request, reads the document and completes the signature in under three minutes. The same-day signing rate exceeds 80% when the request is sent by SMS as well as by email.
Is the electronic signature valid in all EU countries?
Yes: the eIDAS Regulation guarantees mutual recognition of qualified signatures across the entire European Union. Advanced signatures carry probative value in all member states, though the level required for each type of act may vary depending on applicable national legislation.
Does Legalpin act as a certified archive for signed documents?
The record generated by Legalpin includes all elements necessary for the signed document to be independently verified. For long-term archiving with time stamp renewal, Legalpin can advise on document custody options best suited to your compliance requirements.
General information only; this does not constitute individualised legal advice.
