Why password protect a PDF?
PDFs are the standard format for contracts, invoices, legal documents, and confidential reports. Without protection, anyone who receives or finds your file can open, copy, print, or modify it. Adding a password ensures only authorised people can access the content — and you can further restrict what they can do with it.
Common reasons to protect a PDF include sending invoices to clients, sharing legal agreements, distributing confidential reports internally, and submitting sensitive forms.
Step-by-step: Password protect a PDF with PDFKing
Open the Protect PDF tool
Go to pdfking.net/protect.html and click Select PDF File, or drag and drop your PDF onto the upload area.
Enter your open password
Type a strong password in the Open Password field. This is the password anyone will need to open the file. Use the strength meter to guide you — aim for "Strong" or "Very strong".
Optionally set an owner password
An owner password is separate from the open password. It controls permissions — a recipient can open the file with the user password, but only someone with the owner password can change permissions or remove protection.
Set permissions
Use the permission toggles to control whether recipients can print, copy text, or modify the document. By default printing and copying are allowed, modifying is disabled.
Click Encrypt & Download
Your protected PDF is generated entirely in your browser and downloaded immediately. No data is sent to any server.
What encryption does PDFKing use?
PDFKing uses AES-256 encryption via the qpdf library — the same standard used by banks and government agencies. The encryption is applied using the PDF specification's standard security handler, which means the protected file will work with any PDF reader including Adobe Acrobat, Preview on Mac, and browser-based PDF viewers.
Tips for choosing a strong password
- Use at least 12 characters
- Mix uppercase and lowercase letters, numbers, and symbols
- Avoid dictionary words, names, or dates
- Use a password manager to generate and store it safely
- Never send the password in the same email as the protected file
Frequently asked questions
Can I remove the password later?
Yes — use PDFKing's Unlock PDF tool. You'll need the original password to remove protection.
Does this work on Mac, Windows, and mobile?
Yes. PDFKing runs entirely in your browser, so it works on any device with a modern browser — no software installation needed.
Is my file safe?
Your file never leaves your device. All processing happens locally in your browser using JavaScript. PDFKing has no server that receives your documents.
What if the recipient can't open my protected PDF?
Make sure you share the password through a separate, secure channel — such as a text message or phone call. All major PDF readers support AES-256 encrypted files.