How to Digitally Sign a PDF
To digitally sign a PDF, you need a certificate file and its password. The signature is sealed into the file with that certificate. PDFDEN's free digital signature tool signs with your .p12 or .pfx certificate in the browser, and the certificate never leaves your device.
Digital Signature PDF: Sign a PDF with your certificate. Free, and your file never leaves your device.
Open Digital Signature PDFSteps
Open Digital Signature PDF and drop in the finished PDF.
Add your certificate file (.p12 or .pfx with an RSA key) and type its password.
Fill in a reason, location or contact if you want them recorded.
Sign and download the PDF.
Open it in a reader such as Acrobat to see the signer and signature status.
Digital signature or electronic signature?
An electronic signature is a visual mark: your drawn or typed name on the signature line. Sign PDF makes that kind, and the guide on how to sign a PDF covers it. Most everyday agreements accept it.
A digital signature is cryptographic. It uses a certificate to record who signed and to reveal whether the file changed afterward. Readers such as Acrobat show the signer and warn when the document was edited after signing. Some contracts and government forms require this kind.
Check which one the recipient asks for before you sign.
Getting a certificate to sign with
The signature is only as trusted as the certificate behind it. Certificates issued by a certificate authority, or by your employer or government, are the ones recipients usually recognize.
The tool needs the certificate as a file: a .p12 or .pfx containing an RSA key, protected by a password. If your certificate is installed on your computer, most systems let you export it in that format together with its private key.
A self-signed certificate works for testing and internal use, but other readers will flag it as unknown.
Digital Signature PDF: Sign a PDF with your certificate. Free, and your file never leaves your device.
Open Digital Signature PDFCan I digitally sign a PDF with a CAC card?
Not with this tool. A CAC or other smart card keeps the private key on the card, and the key usually cannot be exported to a file. The PDF signing tool only reads .p12 and .pfx files.
For a CAC, use a desktop reader with smart card support. In Acrobat Reader, open the certificate tools, choose to digitally sign, drag a signature box and pick the digital ID from your card when asked. The menu names vary between versions.
Add a visible signature and a digital one
Many people want both: a handwritten-looking signature on the page and a cryptographic seal on the file. Order matters.
Place the visible signature first with Sign PDF, and fill in any fields. If you want those marks locked into the page, flatten the PDF. Apply the digital signature last. Any change after digital signing breaks the seal, and existing digital signatures in a file are not preserved when you sign it again, so one digital signature per file works best.
Check that the signature worked
Open the signed file in Validate PDF Signature. It shows whether the signature is valid and whether the signed bytes are unchanged. It also lists the signer and the certificate issuer.
The check runs offline, so it does not confirm revocation or whether a certificate authority trusts the certificate. The signature also carries no trusted timestamp, so no third party vouches for the signing time. If a recipient needs a timestamped signature, ask which service they accept.