Signing documents online with your clients

Online document signing with your personal training clients works like this: you send them the document through a link, a single-use code sent to their email confirms that the person signing has access to that mailbox, they accept expressly and a record remains of what they signed and when. Before that, decide which documents are worth signing and draft them clearly. And keep in mind what a signature like this proves and what it does not.

Which documents are worth signing

You do not need to sign everything. Sign what, if a disagreement ever arises, you would want to be able to show exactly as it was accepted:

• The terms of service: what it includes, how much it costs, how it is paid, what happens if they cancel and how you communicate. How to draft that part is covered in cancellation policy.
• Specific authorisations: permission for a use that is not part of the service, requested separately and in writing.
• Changes to what was agreed: a new fee, a change of format or of fixed schedule.

What is not advisable is to use signatures for everything. If every message becomes a document to sign, your client will stop reading them, and then the signature loses its meaning.

Before asking for a signature: the document

A signature is worth as much as the document being signed. If your client does not understand what they are accepting, the signature settles nothing when a doubt arises. Some guidelines:

• Short and in plain language. Better one page that gets read in full than five that nobody finishes.
• One subject per document. The terms of service on one side and each authorisation on the other, so that they can accept one thing without accepting the rest.
• Final version. Check the document before sending it: what is signed is exactly that file.
• A title that makes sense, so that a year from now you both know what it is without opening it.

And explain it to them beforehand. Sending a document to be signed without having discussed it turns a formality into a surprise. It fits naturally into onboarding, as we explain in a new client's first week.

What the regulation says about electronic signatures

In the European Union, electronic signatures are governed by Regulation (EU) No 910/2014 (known as eIDAS) on electronic identification and trust services for electronic transactions in the internal market. Its Article 3(10) defines an electronic signature as “data in electronic form which is attached to or logically associated with other data in electronic form and which is used by the signatory to sign”.

The same regulation also distinguishes between the advanced and the qualified electronic signature, with increasing requirements: the qualified signature is an advanced signature created with a qualified signature creation device and based on a qualified certificate.

On its effects, Article 25.1 of the regulation says that “An electronic signature shall not be denied legal effect and admissibility as evidence in legal proceedings solely on the grounds that it is in an electronic form or that it does not meet the requirements for qualified electronic signatures”.

And Article 25.2 adds that “A qualified electronic signature shall have the equivalent legal effect of a handwritten signature”.

In practice: the fact that a signature is electronic does not by itself take away its value, but the regulation only equates the qualified signature with the handwritten one. Which signature a specific document needs depends on the case; if in doubt, consult an adviser.

What an online signature proves and what it does not

An online signature is useful if it leaves a record that can be shown afterwards. For consents concerning personal data, Article 7.1 of the GDPR (known in Spain as the RGPD) says that, where processing is based on consent, “the controller shall be able to demonstrate that the data subject has consented to processing of his or her personal data”.

A good signature record answers four questions:

1. What was signed: the exact document, so that any later change is noticeable.
2. Who: the name they typed and the email with which it was confirmed.
3. When and from where: the date, the time and the connection it was done from.
4. How: that they accepted expressly, not with a mere click.

And what it does not prove: a code sent to an email shows that the person who signed had access to that mailbox, not that they were that person. If a document needs more guarantees, consult an adviser before using a signature like this. The essentials on your clients' data are in data protection for trainers.

Checklist before asking for a signature

1. Is the document in its final version?
2. Does your client have an email they genuinely access?
3. Have you explained what they are signing and why?
4. Do they know they can say no and discuss it with you?
5. Do you know where the signed document and its record will be kept?
6. Is it a document that needs more guarantees? Consult an adviser first.

How Entrenify handles it

1. You request the signature: you upload the document to the client's record and press “Pedir firma” (Request signature). When you request it, the document is shared with them: you cannot sign what you cannot read. The client must have an email in their record.
2. The link reaches them: they receive an email with a link to sign that is valid for one week. From that link they read the document without logging in to their account. In their app, under “Documentos” (Documents), they also see what is pending signature; the signing itself is done from the link in the email.
3. They request the code: a single-use six-digit code is sent to their email and expires after fifteen minutes. The link allows at most five failed attempts; after that it stops being valid.
4. They accept and sign: they type their name and the code and tick the acceptance box. Without express acceptance, nothing is signed.
5. Same document: when signing, the system checks that the file has the same fingerprint as when you requested the signature; if it has changed, the signature is rejected.
6. They can say no: if they do not agree, they can reject it and explain the reason. Whether they sign or not, you receive a notification.

When it is signed, a signature certificate is generated as a PDF, separate from the document, which is stored in the client's documents and which you both can see. It records the SHA-256 fingerprint of the file, the name they typed, the email with which it was verified, the date and time, the IP address, the browser and how many attempts it took.

What it does not do: Entrenify does not attach a legal label to this signature. Its certificate states what was checked and what it does not prove: it does not prove the person's identity, only access to that email mailbox, and the time is the server's, without a third-party timestamp. The rest of the product is on the Entrenify home page (in Spanish).

Sources consulted

Checked on 11 October 2026. We link to the original source so that you can consult the current text.

• Reglamento (UE) n.º 910/2014 del Parlamento Europeo y del Consejo, de 23 de julio de 2014, relativo a la identificación electrónica y los servicios de confianza para las transacciones electrónicas en el mercado interior: artículos 3 y 25. BOE (DOUE).
• Reglamento (UE) n.º 910/2014, texto consolidado: artículos 3 y 25 (comprobación de vigencia). EUR-Lex (Unión Europea).
• Reglamento (UE) 2016/679 del Parlamento Europeo y del Consejo, de 27 de abril de 2016 (Reglamento general de protección de datos): artículo 7. BOE (DOUE).