了解PDF安全：密码与加密

How PDF Security Works

PDFs support two levels of password protection and various permission restrictions. Understanding these helps you protect sensitive documents effectively.

Two Types of PDF Passwords

User Password (Open Password)

This password is required to open and view the PDF. Without it, the document appears as encrypted gibberish.

Use when:

• Only specific people should see the content
• Sending confidential information via email
• Storing sensitive documents in shared locations

Owner Password (Permissions Password)

This password controls what users can do with the PDF after opening it. The document can be viewed without this password, but certain actions are restricted.

Use when:

• You want anyone to view but not edit
• Preventing printing of draft documents
• Protecting against unauthorized copying

Permission Restrictions

With an owner password, you can restrict:

• Printing: Prevent any printing or allow only low-resolution printing
• Copying: Prevent selecting and copying text or images
• Editing: Prevent changes to the document content
• Annotations: Prevent adding comments or filling forms
• Form filling: Control whether forms can be completed

How to Protect Your PDFs

Use our Protect PDF tool to:

1. Upload your PDF document
2. Set a user password (for opening)
3. Optionally set a separate owner password
4. Choose which permissions to allow
5. Download your protected PDF

How to Remove Protection

If you have the password and need to remove protection, use Unlock PDF. This is useful when:

• You're consolidating documents with different passwords
• The password protection is no longer needed
• You want to share without requiring password entry

Security Best Practices

Password Strength

• Use at least 12 characters
• Combine letters, numbers, and symbols
• Avoid dictionary words and personal information
• Use different passwords for different documents

Password Management

• Store passwords in a password manager
• Never send passwords in the same email as the PDF
• Share passwords through a different channel (phone, text)
• Keep a secure record of document passwords

Encryption Levels

Modern PDFs support strong encryption (AES-256). Our tools use the highest available encryption standard for maximum security.

Limitations to Understand

• Screenshots: Copy protection doesn't prevent screen captures
• Re-typing: Someone can always manually re-type content
• Printing workarounds: Print-to-PDF can bypass some restrictions

Password protection adds a strong layer of security but isn't absolute. For highly sensitive materials, consider additional security measures beyond PDF encryption.

When to Use What