Protect PDF
Add password protection to PDF files free. Encrypt PDFs with open password & permissions. 100% browser-based for security.
The PDF encryption tool applies encryption algorithms to PDF content streams, converting document content into a form that can only be accessed with the correct password. This effectively prevents unauthorized users from opening, reading, or modifying document content, and is the standard practice for protecting confidential information. The tool supports multiple encryption levels from legacy RC4 to modern AES, allowing flexible selection based on security needs and compatibility requirements.
Typical use cases include adding password protection to confidential contracts, financial reports, legal documents, and personnel files. By setting a user password to control document access and an owner password to restrict printing, copying, and editing, you can ensure readability while preventing content misuse when distributing documents across organizations.
All encryption operations are performed locally in your browser. PDF files and entered passwords are never uploaded to any server, keeping confidential documents on your device throughout the encryption process. This avoids data breach risks that could come from cloud-based processing, making it ideal for highly sensitive files.
How to Password Protect a PDF
Upload your PDF file
Click the upload area or drag in the PDF file you want to encrypt. Once loaded, you can configure encryption settings locally.
Set user and owner passwords
Enter a user password (needed to open the document) and an owner password (needed to modify permissions). They can be different, or you can set only one.
Choose encryption level and permissions
Select the encryption algorithm (AES-128, AES-256, etc.) and configure permissions such as printing, copying, and editing.
Click encrypt and download
Click the encrypt button, and the tool will process encryption locally before downloading the encrypted PDF to your device.
Core Features
AES Encryption
Supports AES-128 and AES-256 encryption algorithms for modern-level security. AES is the industry standard for PDF encryption, offering significantly stronger protection against cracking compared to legacy RC4.
Dual Password System
User passwords control document access, while owner passwords control permission settings. These can be set to different values, separating access control from rights management for different security tiers.
Permission Control
Restrict printing, text copying, content editing, and form filling. Even users who know the open password cannot perform restricted operations, effectively preventing unauthorized use of content.
Local Encryption
Passwords and file content never leave your device. All encryption computations happen in your browser, eliminating the risk of sensitive data being transmitted over networks or exposed through cloud processing.
| Encryption Algorithm | Key Length | Compatibility | Security Level |
|---|---|---|---|
| RC4 (40-bit) | 40 bits | Legacy readers | Low - not recommended |
| RC4 (128-bit) | 128 bits | Acrobat 5+ | Medium |
| AES-128 | 128 bits | Acrobat 7+ | High |
| AES-256 | 256 bits | Acrobat 9+ | Highest |
Use Cases
Protect Confidential Contracts
Add an open password to contract PDFs to ensure only authorized parties can view the content. When collaborating with multiple parties or sending externally, this prevents unauthorized access or leaks.
Financial Report Encryption
Restrict printing and copying permissions for financial reports to prevent sensitive data from being duplicated and spread. Even if the document is distributed, recipients can only view it without extracting content.
Legal Document Protection
Set passwords on legal documents to prevent unauthorized access. When transmitting sensitive documents such as case materials or draft agreements, ensure only designated recipients can open and read them.
FAQ
What encryption levels does PDF support?
The tool supports RC4 and AES encryption, including 40-bit RC4, 128-bit RC4, AES-128, and AES-256. AES-256 is recommended for maximum security. See the encryption level table for compatibility and security details. Older readers may not support AES-256, so choose based on the recipient’s reader version.
Can I set different passwords for opening and permissions?
Yes. The tool supports separate user passwords (needed to open the document) and owner passwords (needed to modify permission settings). You can set them to different values or set only one. User passwords control document access, while owner passwords control permission management.
Can I re-encrypt an already password-protected PDF?
Yes. First enter the current password to unlock the file locally, then set a new password or change the encryption level. Both unlocking and re-encryption happen locally in your browser — passwords and file content are never uploaded.
What’s the difference between user and owner passwords?
The user password is required to open the document — anyone wanting to view the PDF content needs this password. The owner password is used to modify document permissions (printing, copying, editing restrictions). You can set only a user password (access control only), or both (access control and permissions).
Can encryption be removed from a PDF?
Yes. Enter the password to unlock the encrypted PDF, then save it as an unencrypted version. The unlocking operation is done locally in your browser. Note that removing encryption leaves the PDF without password protection — anyone can open it.
Does encryption affect PDF content or quality?
No. Encryption only processes the PDF content stream — it does not affect display quality or content integrity. The decrypted PDF content is identical to the original. Encryption does not compress, re-encode, or modify the visual content of the document.
Can an encrypted PDF be opened on any device?
Compatibility depends on the encryption level. AES-256 requires a newer PDF reader (Acrobat 9+) to open. If the recipient uses an older reader, you may need to choose a lower encryption level (such as AES-128) for compatibility. See the encryption level table for details.