What is a digital ID?
A digital ID is an electronic credential used to add digital signatures to documents. It combines a certificate, which states who the ID belongs to and who issued it, with a private key that only its owner should be able to use. Digital IDs are often stored as password-protected .p12 or .pfx files.
Also called: Digital certificate, Signing certificate, .p12 or .pfx file
Updated October 15, 2026 · By the PDFZyro team
What's inside a digital ID
The certificate is public. It holds the owner's name, often with an email address or organization, a public key, the dates it's valid between, and the signature of whoever issued it. The private key is secret: it's what actually creates signatures, and anyone who has it can sign as you. That's why a .p12 or .pfx file (the PKCS #12 format) is protected with a password, and why some IDs live on a smart card, a USB token or a hardware security module that the key can't be copied from.
Self-signed IDs and certificate authorities
Anyone can make a self-signed digital ID, with any name, in a few seconds. Its signatures still show whether a document has changed, but PDF readers can't confirm who signed, so they mark the identity as not verified. A certificate authority (CA) checks your identity before it issues an ID, and signs your certificate with its own. PDF readers trust that ID when the CA is on a list they rely on, such as the Adobe Approved Trust List (AATL) or the EU Trusted Lists.
Self-signed IDs suit internal approvals and personal use, where the people involved already know you. For documents sent to people who need to rely on your identity, an ID from a recognized CA is the better choice.
Looking after a digital ID
Digital IDs expire, usually after one to three years, and a CA can revoke an ID whose key was lost or stolen. Signatures made while the ID was valid can still be checked after it expires, more reliably when they include a trusted timestamp, but you need a new ID to sign after that. Use a strong password, keep a backup of the file somewhere safe, and never share it: a digital ID identifies one person.
How to use a digital ID in PDFZyro
- Open Settings, then Digital IDs, and click Create a Digital ID for a self-signed ID in your name, valid for 3 years, or upload a .p12 or .pfx file you already have.
- Open the document, choose Tools, then Sign with a Digital ID, pick your ID, choose what the signature shows and type its password. PDFZyro never stores the password.
- Click Place and sign and drag a box on the page. The signed PDF is saved as a new version, and anyone can check the signature with Check signatures or another PDF reader.
Tools and guides
Related terms
- Digital signatureA cryptographic, certificate-based seal that shows who signed a file and that it hasn't changed.
- Advanced electronic signature (AES)The middle level of e-signature under eIDAS: linked to one signer and tamper-evident.
- Qualified electronic signature (QES)The highest level of e-signature under the EU's eIDAS Regulation, equal in law to a handwritten one.