Sign PDF cryptographically — privacy-first, keys stay local
Your private key never leaves your browser. The server stores only your public key and signature for verification. No document upload required.
Cryptographically signed, tamper-evident, verifiable anywhere.
Secure Signing
Your private key is generated and used entirely in your browser. It never touches our servers.
Tamper-Evident
Every byte of the document is hashed and cryptographically bound to the signature. Any edit breaks the seal.
Verifiable Anywhere
Share a verification link. Anyone can confirm the signature against the public key — no account, no login.
Six steps. Zero uploads.
Open your document
Select a PDF from your device — it stays on your device.
Keys generated locally
A fresh ECDSA P-256 key pair is generated in your browser.
Document hashed
A SHA-256 fingerprint is computed — locally, byte-by-byte.
Signature applied
Your private key signs the hash. It never leaves the browser.
Public key registered
Only the public key and signature go to the server for verification.
Share verification link
Anyone can confirm the signature against the public key — no account needed.
Most signers upload. We sign locally.
- ✕Your document is uploaded
- ✕Provider holds the private key
- ✕Trust depends on the vendor
- ✕Email links, not cryptographic proof
- ✓Document stays on your device
- ✓Private key never leaves the browser
- ✓Client-side key handling
- ✓ECDSA P-256 cryptographic proof
Every agreement, every signer, every workflow
Contracts & NDAs
Cryptographic proof of signing — legally robust receipts.
- Timestamp bound
- Tamper-evident
- Verifier URL
Vendor Agreements
Purchase orders, SOWs, and procurement docs — fully sealed.
- Signer identity bound
- Revocation trail
- Audit-ready
Academic Letters
References, transcripts, and credentials — tamper-evident.
- Institution key ID
- Issued-on timestamp
- Public verification
Proposals & Offers
Sales proposals sealed at send — both parties hold proof.
- Sender + recipient keys
- Delivery receipt
- Offer integrity
Compliance Docs
SOC, ISO, audit replies — tamper-evident by default.
- Hash-anchored
- Exportable receipts
- Auditor-ready
Personal Documents
Letters of intent, IDs, release forms — sealed and shareable.
- Self-signed proof
- Shareable verifier
- Browser-only
No account. No uploads. Just open your PDF.
Private Keys Stay Local. Signatures Stay Provable.
Your private key is generated locally and never shared. The server only holds the public key, signature, and document hash — enough to verify, never enough to impersonate.
- ✓Encrypted signing in the browser
- ✓Server only sees the public key and signature
- ✓Document bytes never uploaded
- ✓Integrity verification for every signature
Signing PDFs — common questions
Is a PDF Pro signature legally binding?
For most contracts, yes. PDF Pro produces an Advanced Electronic Signature: a cryptographic signature using ECDSA P-256 keys generated in your browser, with a SHA-256 hash of the document and a timestamp. This satisfies the requirements for electronic signatures under the U.S. ESIGN Act, the EU eIDAS regulation (Article 26), and similar laws in the UK, Canada, Australia, and most jurisdictions.
Documents that legally require a Qualified Electronic Signature (a small subset of EU contracts — typically real estate, wills, or notarized agreements) need a Qualified Trust Service Provider, which PDF Pro is not.
How does verification work?
Every signed PDF gets a verification link (e.g. /sign?mode=verify). Anyone with the link — recipient, lawyer, court — can open it, drop the signed PDF in, and instantly confirm three things: (1) the file hasn't been modified since signing, (2) the signature matches the public key that signed it, and (3) the signing timestamp. All checks run client-side, so the verifier doesn't upload the document either.
Where is my signing key stored?
In your browser's IndexedDB, encrypted with a passphrase you choose. The private key never leaves your device. We don't have a copy. If you lose the device or clear browser storage without exporting your key first, the key is gone — the signed documents remain valid (verification only needs the public key embedded in the signature) but you can't sign new documents with the same identity.
Can I draw, type, or upload an image of my signature?
Yes — those are the visible signature appearance options. You can draw a signature with a mouse or touchscreen, type a name in a script font, or upload a transparent PNG of your handwritten signature. Independent of the visual appearance, the cryptographic signature is what makes the document tamper-evident.
Does it create an audit trail?
Yes. Each signature embeds a JSON metadata block with: signer name, signer email (if provided), timestamp (ISO 8601 UTC), signing IP region (country-level only, no logging), document SHA-256 hash, and signer's public key. Anyone verifying the document sees the full audit trail without contacting our servers.
Can multiple people sign the same PDF?
Yes — sequentially. Sign first, share via Secure Transfer (or email the signed PDF directly), and the next signer drops it into PDF Pro's Sign tool. Each new signature appends a fresh signed block while preserving every prior signature, so the verification page shows all signers and their timestamps.
What about timestamp authority and long-term validity?
The default timestamp is the signer's local clock. For legally archived documents that need a trusted third-party timestamp (RFC 3161), connect to an external TSA via the advanced signing options — PDF Pro embeds the TSA response into the signature so verification works decades later.
Your Signature, Your Proof.
Nothing leaves your browser.
Drop a PDF. Sign it locally. Share a verification link in seconds.