How to encrypt a PDF file in 2025

Sending a confidential contract or financial report as a PDF without encryption is like mailing a postcard—anyone who intercepts it can read your sensitive information. PDF encryption protects your documents by requiring a password to open them, preventing unauthorized access even if the file is shared, lost, or stolen.

PDF encryption transforms your document into unreadable code that can only be decrypted with the correct password. Whether you're protecting business contracts, financial reports, or personal documents, encrypting PDFs adds a crucial security layer. This guide covers multiple methods to encrypt PDF files, from built-in tools to secure cloud-based solutions with advanced protection features.

Quick recap of PDF encryption methods

1. Adobe Acrobat: Professional PDF encryption with password protection and permission restrictions
2. Online PDF tools: Free web-based encryption services for quick password protection
3. Built-in OS tools: Use Preview (Mac) or Microsoft Office to create encrypted PDFs
4. Secure sharing platforms: Use Papermark for encrypted PDF sharing with analytics and access controls
5. Command-line tools: Advanced encryption using PDFtk or QPDF for batch processing

Method 1: Encrypt PDF using Adobe Acrobat

Adobe Acrobat provides the most comprehensive PDF encryption options with strong security features.

Step-by-step guide for encrypting PDFs with Adobe Acrobat:

1. Open your PDF in Adobe Acrobat (Pro or Standard)
2. Navigate to security options:
   • Go to File > Protect Using Password (or Tools > Protect > Encrypt > Encrypt with Password)
   • Alternatively, click All tools > Protect a PDF in the left pane
3. Choose encryption type:
   • Select "Encrypt with Password"
   • Choose whether to require password for viewing, editing, or both
4. Set password protection:
   • Check "Require a password to open the document"
   • Enter a strong password (minimum 8 characters, mix of letters, numbers, and symbols)
   • Confirm the password
5. Configure permissions (optional):
   • Restrict printing (allow or disallow)
   • Restrict editing (allow or disallow)
   • Restrict copying of text and images
   • Restrict document assembly
6. Choose encryption level:
   • AES-256 (recommended for maximum security)
   • AES-128 (faster, still secure)
   • 128-bit RC4 (older, less secure)
7. Click "OK" and save the encrypted PDF

Adobe Acrobat uses industry-standard AES encryption, making it extremely difficult for unauthorized users to access your PDF without the password. The permissions settings allow you to control what recipients can do with the document even after opening it.

Note: Adobe Acrobat Pro requires a paid subscription. For free alternatives, see Method 2 or Method 4.

Method 2: Encrypt PDF using online tools

Free online PDF encryption tools provide quick password protection without installing software.

Using Adobe's free online tool:

1. Visit Adobe's password protect PDF tool
2. Upload your PDF file by clicking "Select a file" or dragging and dropping
3. Enter a password in the password field
4. Confirm the password by entering it again
5. Click "Protect PDF" to encrypt the file
6. Download the encrypted PDF once processing is complete

Using other online PDF encryption services:

Popular free online tools include SmallPDF, ILovePDF, and PDF24. The process is similar across platforms:

1. Visit the encryption service website
2. Upload your PDF file
3. Set encryption options: Choose password protection and permission restrictions
4. Enter and confirm a strong password
5. Click encrypt or protect to process the file
6. Download the encrypted PDF

Security considerations: Be cautious when using online tools with highly sensitive documents. These services process files on their servers, which means your PDF content is temporarily accessible to the service provider. For confidential business documents, consider using local software or secure file sharing platforms that offer better privacy controls.

Method 3: Encrypt PDF using built-in OS tools

Both Mac and Windows include built-in tools that can create encrypted PDFs without additional software.

Mac: Encrypt PDF using Preview

1. Open your PDF in Preview (default PDF viewer on Mac)
2. Go to File > Export (or press Command + Shift + E)
3. Click the "Permissions" button in the export dialog
4. Set encryption options:
   • Check "Require password to open document"
   • Enter a strong password and confirm it
   • Optionally restrict printing and copying
5. Choose encryption level: Select "128-bit RC4" or "AES-128"
6. Click "Save" to create the encrypted PDF

Preview uses AES-128 encryption, which provides strong security for most use cases. The encrypted PDF will require the password to open, and you can set additional restrictions on printing and copying.

Windows: Create encrypted PDF from Office documents

If you have Microsoft Office, you can create encrypted PDFs directly:

1. Open your document in Word, Excel, or PowerPoint
2. Go to File > Save As (or Export)
3. Choose PDF format from the file type dropdown
4. Click "Options" before saving
5. Check "Encrypt the document with a password"
6. Enter a password and confirm it
7. Click "OK" and save the PDF

This method creates a password-protected PDF that requires the password to open. However, it doesn't offer the same granular permission controls as Adobe Acrobat.

Method 4: Encrypt PDF using Papermark

Papermark provides a secure way to encrypt and share PDFs with advanced security features beyond basic password protection, including analytics, access controls, and dynamic watermarking.

Step-by-step guide for encrypting PDFs with Papermark:

1. Create your Papermark account:

   • Visit Papermark
   • Sign up for a free account or log in
   • Access your secure dashboard

2. Upload your PDF:

   • Click "Upload Document" or drag and drop your PDF file
   • Papermark automatically encrypts files during upload using AES-256 encryption
   • Supports PDFs of any size

3. Configure encryption and security settings:

   • Navigate to document settings
   • Enable password protection and set a strong password
   • Toggle email verification to require recipient identity confirmation
   • Set access expiration dates to limit file accessibility
   • Configure allowlist/denylist to control who can access the PDF

4. Enable advanced protection features:
   • Activate dynamic watermarking to add recipient information to each page
   • Toggle download prevention to allow viewing only
   • Configure screenshot protection to discourage unauthorized captures
   • Set custom permissions for different recipients
   • Enable NDA gate before access for additional legal protection

5. Share the encrypted PDF:
   • Generate a secure, encrypted link
   • Share the link via email or messaging
   • Provide the password through a separate, secure channel
   • Monitor access through Papermark's page-by-page analytics dashboard

Papermark uses server-side AES-256 encryption combined with comprehensive access controls. While it doesn't use end-to-end encryption, it provides strong security with the added benefit of document analytics, engagement tracking, and access revocation—making it ideal for business use cases where you need to track who viewed your PDF and when.

Encrypt and share PDFs securely

Method 5: Encrypt PDF using command-line tools

For advanced users or batch processing, command-line tools provide programmatic PDF encryption.

Using PDFtk (Windows/Mac/Linux):

1. Install PDFtk from pdflabs.com
2. Encrypt a PDF using the command line:

   pdftk input.pdf output encrypted.pdf user_pw password123
   

3. Set owner password (for permissions):

   pdftk input.pdf output encrypted.pdf user_pw password123 owner_pw ownerpass
   

4. Set permissions (restrict printing, copying):

   pdftk input.pdf output encrypted.pdf user_pw password123 allow Printing
   

Using QPDF (Linux/Mac):

1. Install QPDF using package manager:

   # Mac
   brew install qpdf
   
   # Linux
   sudo apt-get install qpdf
   

2. Encrypt PDF:

   qpdf --encrypt user-password owner-password 256 -- input.pdf output.pdf
   

3. Set restrictions:

   qpdf --encrypt user-password owner-password 256 --modify=none --print=none input.pdf output.pdf
   

Command-line tools are powerful for automating PDF encryption across multiple files but require technical knowledge to use effectively.

Comparison: PDF encryption methods

Best practices for PDF encryption

Follow these practices to maximize the security of your encrypted PDFs.

1. Use strong passwords: Create passwords with at least 16 characters, mixing uppercase, lowercase, numbers, and special characters. Avoid dictionary words, personal information, or common patterns. Consider using a password manager to generate and store strong passwords.

2. Backup passwords securely: Always store passwords in a secure location separate from your encrypted PDFs. Use a password manager or encrypted note-taking app. Never share passwords in the same email or message as the PDF link.

3. Choose appropriate encryption strength: For highly sensitive data, use AES-256 encryption. For less sensitive files, AES-128 may be sufficient and faster. Avoid older encryption standards like 40-bit RC4, which are no longer considered secure.

4. Set appropriate permissions: Configure document permissions based on your needs. Restrict printing, copying, or editing if recipients don't need these capabilities. This adds an extra layer of protection even if someone gains access to the PDF.

5. Verify encryption is working: Test that encrypted PDFs cannot be opened without the correct password before relying on encryption for sensitive data. Try opening the file without the password to confirm protection is active.

6. Combine encryption with other security measures: Encryption protects PDFs at rest, but also use secure transmission methods (HTTPS, secure email), access controls, and consider dynamic watermarking for additional protection against unauthorized sharing.

Conclusion

Encrypting PDF files protects your sensitive documents from unauthorized access, whether they're stored locally or shared online. Choose Adobe Acrobat for professional-grade encryption with granular permissions, online tools for quick password protection, or Papermark for encrypted PDF sharing with analytics and advanced access controls. For business use cases where you need to track access and control sharing, Papermark's secure PDF sharing provides encryption plus comprehensive security features.

Start encrypting your PDFs

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