PDF Security

Password protect, watermark, unlock, and digitally sign PDFs. All security operations happen in your browser — your confidential documents never leave your device.

AES-256 EncryptionLegally Valid E-SignaturesVisible WatermarksNo Server Upload
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Password Protect PDF

AES-256 encryption — strongest standard available

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Unlock PDF

Remove owner restrictions from PDFs you own

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Watermark PDF

Mark CONFIDENTIAL, DRAFT, or custom branding

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Sign PDF

Legally valid electronic signature

PDF Security Layers Explained

User Password (Encryption)

Prevents the document from being opened without the correct password. PDFFlow applies AES-256 — the strongest available standard. Nobody can read the content without the password.

Owner Restrictions

Allows the document to open freely but disables specific functions — printing, copying text, editing. Lower security than encryption but useful for controlling document use.

Visual Watermarks

Text burned permanently into page content. Cannot be removed by standard tools. Communicates document status (DRAFT, CONFIDENTIAL) and deters unauthorized redistribution.

Electronic Signature

Visual signature embedded in page content. Legally valid for most commercial agreements. Does not create a timestamped audit trail — use certified services for regulated transactions.

When to Use Each Security Tool

ScenarioTool
Sending salary letter by emailProtect PDF
Sharing draft proposal with clientWatermark PDF
Contract received from clientSign PDF
PDF blocks printingUnlock PDF
Sending medical recordsProtect PDF
Distributing paid contentWatermark + Protect
NDA for signatureSign PDF
Internal policy distributionWatermark PDF

Frequently Asked Questions

How do I password protect a PDF for free?+
Use PDFFlow Protect PDF. Upload your PDF, enter and confirm a password, and download the AES-256 encrypted file. Works in any browser on any device. Files processed locally — your password and document never reach any server.
Is AES-256 PDF encryption secure?+
AES-256 is the encryption standard used by banks, governments, and enterprise security systems. It is computationally infeasible to brute-force with current technology. A well-chosen password makes an AES-256 encrypted PDF effectively inaccessible without the correct credentials.
How do I remove a password from a PDF?+
If you own the PDF and have the password, use PDFFlow Unlock PDF to remove the encryption. For PDFs with only owner restrictions (that open freely but block printing/copying), Unlock PDF removes those without requiring a password.
What is the difference between a watermark and a password?+
A password (encryption) prevents the document from being opened at all without credentials. A watermark is a visible marking burned into page content — it communicates DRAFT, CONFIDENTIAL, or ownership without blocking access. Use passwords for genuine security; use watermarks for status communication and IP protection.
Are electronic signatures on PDFs legally valid?+
Yes, under US ESIGN Act, EU eIDAS, and equivalent legislation in most countries. Visual electronic signatures from PDFFlow are legally valid for standard commercial contracts, NDAs, employment agreements, and leases. Regulated industries requiring certified signatures with audit trails should use DocuSign or Adobe Sign.
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Digital Signatures

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PDF Editing

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Document Productivity