Sello

macOS · PDF

Sign PDFs on your Mac.

Sign PDFs with your digital certificate in macOS Keychain. Open the document, place your signature, and save.

Coming soon to the Mac App Store 5 € · paid once

Apple Silicon · macOS Tahoe 26 or later

On your Mac.

Your PDFs stay with you.

With your certificate.

Your private key stays in Keychain.

One purchase.

€5. No subscription.

How it works

Open. Sign. Save.

01

Open your PDF

Drop it into Sello or choose it from Finder. You can add a signature to an already signed document when its permissions allow it.

02

Choose your certificate

Select a certificate with its private key in Keychain. Place a visible stamp, or sign without one.

03

Sign and save

Choose a destination and approve key access if macOS asks. Your document is signed locally.

Your documents stay on your Mac.

Sello does not upload your documents, export your private keys, or require a Sello account. Signing and integrity checks happen on your Mac.

What you need to know

Does it work with FNMT certificates?

Yes. We have tested FNMT software certificates installed in Keychain. You need both the certificate and its private key. DNIe, smart cards and other hardware tokens have not been validated.

Does it replace AutoFirma?

Sello signs local PDF files. It does not handle afirma: links or integrate with web procedures that require AutoFirma. It also does not sign standalone XAdES or CAdES files.

What kind of signature does it create?

PAdES Baseline B-B PDF signatures. It checks local integrity and preserves already signed bytes when adding another signature. It does not obtain trusted timestamps or fetch revocation information or EU trusted lists.

Will every authority accept it?

Acceptance depends on the procedure and its requirements. Tested documents could be inspected in AutoFirma and several passed VALIDe. These results do not guarantee acceptance everywhere.

Which Mac do I need?

An Apple Silicon Mac running macOS Tahoe 26 or later. This first release does not support Intel Macs. Encrypted PDFs are not supported.

Need a hand?

Certificate setup, questions, or trouble signing a document.

contact@negativeepsilon.com