Digital Signature
Apply a cryptographic digital signature to a PDF using an X.509 certificate in PFX, P12 or PEM format, with a visible signature and timestamp.
Upload PDF to Sign
About This Tool
A drawn signature is a picture. It proves nothing about who applied it and nothing about whether the document changed afterwards. A digital signature is different: it uses a private key to produce a cryptographic seal over the document contents, which establishes both identity and integrity.
If a single byte changes after signing, verification fails. That is what makes digital signatures acceptable where a legal or regulatory standard requires proof rather than the appearance of one.
Certificates in PFX, P12 and PEM formats are supported. You can include a visible signature block on the page, a stated reason for signing, a location, and a timestamp establishing when the signature was applied. The private key is used in your browser and never transmitted.
How to Use
Load the PDF
Drop in the document to be signed.
Provide your certificate
Upload a PFX, P12 or PEM file and enter its password.
Configure the signature
Choose whether it appears on the page, and set the reason, location and timestamp.
Sign and download
Save the signed PDF. Any subsequent change will invalidate the signature.
Use Cases
Legally significant agreements
Contracts where a cryptographic signature is required rather than an image of one.
Regulatory submissions
Filings that mandate a certificate-based signature.
Tamper-evident documents
Certificates and official records where any later modification must be detectable.
Frequently Asked Questions
How is this different from Sign PDF?
Sign PDF places an image of your signature. This applies a cryptographic seal using your private key, which proves identity and detects any later change.
Where do I get a certificate?
From a certificate authority, or your organisation IT if it operates its own. Self-signed certificates work technically but are not trusted by default in readers.
Is my private key uploaded?
No. The certificate is used in your browser and neither the key nor its password is transmitted.
What happens if the document is edited afterwards?
Verification fails and readers show the signature as invalid. That is the intended behaviour.