Table of contents
- What is a digital signature and what is it for
- How to obtain a digital signature
- How to digitally sign a PDF
- How to create a digital signature with SPID
- Types of electronic signatures: differences and uses
- Tips for using digital signatures safely
Knowing how to create a digital signature is now essential for anyone managing documents online. Contracts, electronic invoices, self-certifications, or administrative applications everything can be digitally signed without printing a single page. But how exactly does an electronic signature work? What are the differences between the various types of signatures? And above all, how can you digitally sign a PDF or use SPID to do it easily and securely?
In this practical guide, we’ll walk you step by step through how to obtain a legally valid digital signature, how to sign a PDF document, and how to use SPID to apply a qualified electronic signature.
What is a digital signature and what is it for
A digital signature is a specific form of qualified electronic signature that guarantees both the signer’s identity and the integrity of the document. In simple terms, applying a digital signature ensures that the file truly comes from the person who signed it and that it has not been altered after signing.
From a legal standpoint, it has the same value as a handwritten signature on paper, as long as it is created using recognized tools certified by an authorized body.
The rules governing digital signatures are established by the Italian Digital Administration Code (CAD) and the EU eIDAS Regulation, which recognize their legal validity in all EU member states.
It can be used to:
- sign employment or supply contracts;
- submit applications to public administrations;
- send tax returns or corporate financial statements;
- sign digital notarial deeds or professional documents.
How to obtain a digital signature
To obtain a digital signature, you need to contact a certified provider accredited by the Agenzia per l’Italia Digitale (AgID) such as Aruba, InfoCert, PosteID, Namirial, or Actalis. Each provider offers different solutions based on user needs.
The main types are:
- Digital signature with USB token or smart card
This is the traditional method. After receiving the signing kit, you install the provided software on your computer and connect the USB token or smart card reader. Once your personal digital certificate is loaded, you can sign documents directly from your PC. - Remote digital signature
This is a more modern and practical option, as it doesn’t require any physical device. You log in to your provider’s online service using your credentials and confirm each signature with a one-time password (OTP) sent via SMS or app. It’s perfect for those who work on the go and use mobile devices. - Digital signature with SPID
Some providers allow you to digitally sign using SPID, your digital identity. In this case, authentication is done through the SPID system, and the signature is considered a qualified electronic signature, fully valid under the law.
How to digitally sign a PDF
One of the most common uses is signing a PDF file. This can be done using the software provided by your certification provider or through dedicated web services.
Here are the general steps:
- Open the signing software or your provider’s portal.
- Upload the PDF document you want to sign.
- Select digital signature and choose the certificate type.
- Enter your PIN or OTP code to confirm the operation.
- Download the digitally signed file, which will either have a .p7m extension or display a visual seal on the PDF.
The signed document retains full legal validity, as it includes the digital certificate and a timestamp, which certify the exact date and time of signing.
Example
If you digitally sign a consulting contract in PDF format, there’s no need to print or mail it. You can send it via PEC (certified email) or store it in a digital archive it will be legally binding.
How to create a digital signature with SPID
Today, many platforms allow you to apply a digital signature using SPID. It’s a completely online process quick, secure, and ideal for those who prefer not to purchase a physical kit.
Here’s how it works:
- Go to the website of a certified provider (e.g., InfoCert, Namirial, or PosteID).
- Choose “Sign with SPID” or “Remote signature.”
- Log in with your SPID account.
- Upload the PDF document you want to sign.
- Enter the OTP code received via SMS or app.
- Download the digitally signed file.
This type of signature has full legal validity because SPID guarantees the signer’s identity and the provider ensures the traceability of the entire process. It also works on any device computer, smartphone, or tablet.
Types of electronic signatures: differences and uses
Not all electronic signatures are the same. The EU eIDAS Regulation defines three main levels:
- Simple Electronic Signature (SES)
Could be a checkbox on a form or a drawn signature with a mouse low evidentiary value. - Advanced Electronic Signature (AES)
Uniquely links the signature to the signer and enables identification but doesn’t always have full legal effect. - Qualified Electronic Signature (QES)
The true digital signature, the only one equivalent to a handwritten signature.
Only the qualified electronic signature provides guaranteed legal validity for contracts and official documents.
Tips for using digital signatures safely
To keep your digital signature secure, it’s important to:
- Store your USB token or smart card safely;
- Never share your PIN or OTP code;
- Regularly update your signing software;
- Always verify that the signed document includes a valid timestamp and certificate;
- Use only AgID-accredited services to sign or verify PDF files.
These precautions ensure that your electronic signature cannot be misused and that your digital documents remain protected from tampering.
In summary
Today, creating a digital signature is quick, easy, and secure. Whether you choose a remote signature, SPID, or USB token, the result is a legally valid document signed in seconds. Qualified electronic signatures represent a major step toward the full digitalization of citizens, businesses, and public administrations.
