PDF Tool
Digitally Sign PDF
Add a cryptographic PKCS#7 digital signature to a PDF, with a visible signature box you place on any page or with nothing added to the pages. Generate a self-signed certificate in your browser or use your own .p12/.pfx certificate.
Drop your file here, or browse
The PDF you want to sign
Related tools
How to Digital Signature PDF
Add your PDF
Drop the PDF you want to sign. It opens large, with its pages beside it.
Choose a certificate and the box
Generate New makes a self-signed certificate in your browser; Upload Existing opens your .p12/.pfx file with its password (press Load). Keep Visible signature box and drag the box where it should go on any page, or choose Invisible signature.
Sign and download
Press "Add digital signature". The signed page is shown with what was checked on the file; press "Download PDF" to save it.
Features
- PKCS#7 detached digital signatures
- In-browser RSA-2048 key & certificate generation
- Upload existing .p12/.pfx certificates
- SHA-256 hash of document content
- Private key never stored or transmitted
- Visible signature box you place on any page, or none at all
- Placed exactly where shown, on rotated and cropped pages too
- Checks the signed file: whole-file byte range, digest, RSA signature
Frequently Asked Questions
What is the difference between a visual signature and a digital signature?
A visual signature is just an image stamped on the PDF. A digital signature is cryptographic: it records which certificate signed the document and shows whether the document was modified after signing. Whether that certificate proves who the signer is depends on who issued it.
Can I use my own company certificate?
Yes, if it is a .p12 or .pfx file with an RSA key. Choose Upload Existing, add the file, type its password and press Load: the name, issuer and expiry date are shown, and the document is signed with that certificate's private key. The file and its password are only used in your browser.
Can I choose where the signature appears?
Yes. With Visible signature box, a box showing the signer's name, the date and the algorithm is drawn on the page: drag it, pull a corner to resize it, move it to any page, or type its position and size in millimetres. It is written exactly there, on rotated and cropped pages too. Choose Invisible signature to add nothing to the pages.
Will a PDF reader trust the signature?
That depends on the certificate, not on the file. A self-signed certificate is not trusted until the person opening the file chooses to trust it; a certificate from an authority the reader already trusts can be. After signing, Docukit checks the signed file in your browser: the signature covers the whole file, the SHA-256 digest matches and the RSA signature verifies. It does not check trust.
Is my private key secure?
Your private key is only used inside this page to sign. It is never uploaded, stored or sent anywhere. A key made with Generate New is offered to you as a .p12 file after signing and is not kept anywhere else.