Digitally signing a PDF document is an increasingly frequent necessity today: contracts, declarations, legal documents, quotes, and much more require a legally valid signature. But how do you create a digital signature? What is the difference compared to a simple electronic signature? And what tools are needed to sign a PDF securely and in compliance with regulations?
In this guide, we explain what a digital signature is, how to obtain one in Italy, and how to correctly apply it to a PDF file, step by step.
What is a Digital Signature?
A digital signature is a type of qualified electronic signature that guarantees the authenticity, integrity, and non-repudiation of a document. It has full legal value and is regulated by the eIDAS regulation at the European level and by the Digital Administration Code (CAD) in Italy.
Compared to a handwritten signature on paper, a digital signature:
- is uniquely linked to the signatory
- is generated through a qualified digital certificate
- is affixed using secure devices (tokens, smart cards, USB drives, or apps)
- can be verified at any time by third parties
Digital Signature vs. Electronic Signature
Be careful not to confuse a digital signature with a simple electronic signature (such as a scanned handwritten signature or the use of a drawing tool). The latter does not have independent legal value and does not guarantee the origin of the document. Only a qualified digital signature is recognized by law as equivalent to a handwritten signature.
How to Obtain a Digital Signature in Italy
To create a digital signature, you need a digital signature kit, which you can obtain from an accredited certifier. Among the most well-known in Italy are:
- Aruba
- InfoCert
- Namirial
- Poste Italiane
- CNS/Smart Card from the Chamber of Commerce
The activation process can take place online (via SPID, video identification, or PEC) or in person. Once you have obtained the certificate, you can digitally sign your PDFs using dedicated apps, software, or devices.
Tools for Digitally Signing a PDF
Once you have the signature certificate, you can use various tools to affix the signature to a PDF file:
1. Sign with Provider Software
Each provider (e.g., ArubaSign, Dike, FirmaCerta) offers its own free software for signing PDFs in a compliant manner.
2. Sign with Mobile App
Some providers offer apps that allow you to sign directly from your smartphone, using OTP or biometrics.
3. Sign with Adobe Acrobat Reader
Adobe supports digital signatures only if you have already installed a qualified certificate on your system. The file is signed in PAdES format, recognized as valid.
4. Sign Online via Cloud Services
There are web platforms such as firma.infocert.it or Aruba Firma Online that allow digital signing directly online.
Digital Signature Format: PAdES, CAdES, XAdES
When you digitally sign a PDF, the most common format is PAdES (PDF Advanced Electronic Signatures). This standard:
- keeps the PDF file readable
- integrates the signature within the document
- allows for the coexistence of multiple signatures
Other formats used for digitally signing non-PDF files are CAdES (extension .p7m) and XAdES for XML files.
How to Apply a Digital Signature to a PDF
Here is an example of a standard procedure with signing software:
- Open the software (e.g., ArubaSign, Dike GoSign)
- Import the PDF document to be signed
- Choose the signature type (PAdES for PDF)
- Select the digital certificate to use
- Enter the PIN or confirm with OTP
- Save the signed document
The file will now be legally signed and ready to be sent, archived, or delivered.
How to Verify a Digital Signature on a PDF
Recipients of a digitally signed PDF document can verify its validity through:
- Adobe Acrobat Reader (displays “Valid Signature” message)
- The provider’s signing software
- Online services such as InfoCert’s Signature Verification
Does a Digital Signature Expire?
Yes, each certificate has an expiration date (usually 1, 2, or 3 years). However, signed documents remain valid even after the expiration date, provided that the signature was valid at the time of affixing. To preserve documents over time, a timestamp is used.
FAQ: Frequently Asked Questions
Is a digital signature mandatory for contracts?
No, but in many cases, it is preferable. For documents with legal value, tenders, electronic procedures, or contracts between companies, a digital signature is the most secure and recognized form.
Can I sign digitally with SPID?
SPID is not a digital signature, but some platforms allow the activation of one-shot digital signatures through SPID authentication.
Is a scanned signature valid?
A scanned handwritten signature does not have independent legal value. It can be used for informal agreements but is not comparable to a qualified digital signature.
Conclusions
Creating a digital signature for PDFs is an essential step for anyone working with electronic documents who wants to ensure legal validity, integrity, and security. Obtaining a certificate is simple, and today there are tools accessible to everyone, even from smartphones. If you send important documents, contracts, or official communications, learning to sign them digitally is a skill that can no longer be lacking.
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