Password Protect PDF Securely (AES-256 & 100% Offline)
Add AES-256 password protection to your PDF files instantly. 100% private, encrypted entirely in your browser.
Drag & Drop your PDF files here
or click to browse files
Related PDF Tools
Common Use Cases for PDF Encryption
Finance & Accounting
Secure tax returns, bank statements, and invoices with AES-256 before emailing them to accountants or clients.
Legal & Contracts
Protect NDAs, client agreements, and intellectual property documents to ensure only authorized parties can view them.
HR & Personal Records
Lock medical records, payroll data, and identity documents to maintain strict HIPAA compliance and privacy.
Why Use Our Zero-Knowledge PDF Encryptor?
Most online PDF lockers require you to upload your sensitive documents to their cloud servers to apply encryption. This exposes your financial records, legal contracts, or personal data to massive privacy risks.
We built this tool differently. Our Lock PDF tool utilizes Zero-Knowledge architecture. The encryption algorithm runs entirely inside your browser's local memory using JavaScript. Your document is never uploaded to the internet, and we have zero access to your files or passwords.
How to Password Protect a PDF File
Upload
Drag and drop your PDF files into the secure drop zone above.
Set Password
Enter a strong password. This password will be required for anyone trying to view the document.
Download
Click lock. The system encrypts the document instantly using AES-256 for you to download securely.
Security Considerations & Best Practices
When securing a document, your password is the only line of defense against brute-force attacks. We recommend using a minimum of 12 characters, mixing uppercase letters, numbers, and symbols. Since this is an offline tool, you can safely use your password manager to generate and store a strong, random password.
Please remember that PDF password protection prevents unauthorized opening, but if someone has the password, they will have full access. Always share passwords via a separate, secure channel (like an encrypted messaging app) rather than sending them in the same email as the locked PDF.
Frequently Asked Questions
Is it safe to password protect PDFs online?
Yes, absolutely safe. Unlike most online PDF tools that upload your sensitive documents to a remote server, our tool uses Zero-Knowledge Client-Side Processing.
This means the entire AES-256 encryption process happens locally right inside your web browser. Your file is never uploaded, transferred, or saved on any server. Your privacy is 100% guaranteed.
How to put a password on a PDF for free?
To put a password on a PDF for free, simply drag and drop your file into our secure tool, type your desired password, and click 'Lock & Download PDF'. The encryption happens instantly in your browser at no cost.
What if I forget the password I set?
It is crucial that you remember or safely store the password you set. Because we use strong AES encryption, a forgotten password means you will not be able to open the encrypted file again. Our servers never see or save your password, so we cannot help you recover it.
Can I remove the password later?
Yes. If you know the password and wish to remove it so you do not have to type it every time, you can use our secure Unlock PDF tool. Just like this tool, it operates entirely offline in your browser.
How do I lock a PDF on Mac, Windows, or Mobile?
Because our tool is entirely web-based, you can lock a PDF on any operating system (Mac, Windows, iOS, Android) without installing any heavy software like Adobe Acrobat. Simply open this page in your web browser, upload your file, and set the password.