Sign PDFs privately.
Prove they're untouched.
OpenSigner adds your signature and seals every document with a SHA-256 fingerprint, right on your device. Nothing is uploaded and there's no account. Anyone can check later that the file wasn't changed.
Priya Sharma
VALID · untouched
sha256 9f2c…e41a
How it works
Three steps. About thirty seconds.
Open your PDF
Drop a file in. It is read into this tab's memory and never sent to a server. Password-protected PDFs work too.
Place your signature
Draw, type or upload a signature, then add initials, a date or text. Drag and resize each one into place on any page.
Seal & download
OpenSigner adds a completion certificate with a QR code, seals the file with SHA-256, and downloads it to your device.
Privacy & security
Your documents stay on your device.
Most e-signature services upload your contracts, consent forms and IDs to their servers. OpenSigner can't, because it has no place to receive them. Rendering, signing and hashing all run in your browser's sandbox.
Our servers only deliver the app's code and, if you buy Pro, handle the payment and license. They never see your documents.
Local processing
pdf.js renders in a Web Worker; pdf-lib writes the result.
Native WebCrypto
SHA-256 is computed by your browser's built-in crypto.subtle.
Offline-ready
After the first visit, the app is cached and runs without a connection.
Verifiable
Every certificate links to a verifier that anyone can use for free.
Frequently asked questions
Is my document really never uploaded?
Yes. OpenSigner reads your PDF with your browser's File API, renders it with pdf.js and writes the signed copy with pdf-lib, all in this tab's memory. There is no upload endpoint for documents. You can check this yourself: load the page, turn off Wi-Fi, and sign. Everything still works.
Is this a legally valid signature?
OpenSigner creates a simple electronic signature with tamper evidence: your signature mark, a completion certificate and a SHA-256 seal. Many everyday agreements accept this kind of signature. It is NOT an Aadhaar eSign, a DSC/certificate-based digital signature, or a qualified electronic signature (QES), and some documents legally require one of those. If you are unsure, ask a lawyer about your specific document.
What does the tamper seal prove?
It proves that the file has not changed, not even by one byte, since it was sealed. It does not, on its own, prove who signed it. Anyone can seal a new file. For stronger assurance, share the seal or the certificate's QR link with the other party when you send the document.
Why can't a PDF contain its own hash?
Writing a hash into a file changes the file, which changes its hash. OpenSigner uses the same trick as PDF digital signatures: it reserves a fixed-length slot, hashes the file with that slot zeroed, then fills in the slot without moving any other byte. The verifier repeats exactly that calculation.
Does it work with password-protected PDFs?
Yes. You enter the password locally to open the file. Because encrypted files can't be edited in place, the signed copy is rebuilt from high-resolution page images and saved without a password.
What happens if I edit the PDF after signing?
Verification will fail with a red "Tampered" result. If the file is re-saved by another app, the seal may be stripped completely, and the verifier will report that no seal was found.
What do I get with Pro?
Your own logo and company details on the certificate, no OpenSigner branding, and saved field templates for forms you sign often. It costs ₹3,999 a year (about ~$49). The free plan has no document limits.