PureTools
Password-Protect Your PDF, Free & Private
Add AES-256 password protection to any PDF entirely in your browser. Set your password, click Protect, and download the secured file. No upload, no watermark, works offline, no signup.
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Files up to 100 MB. Your file stays on your device.
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Download protected PDFHow to password-protect a PDF
The PDF Password Protector adds AES-256 encryption directly to your file inside your browser tab. No account is needed, nothing is uploaded, and no watermark is added. The protected PDF works in every major viewer: Adobe Acrobat, Chrome, Edge, Firefox, Preview on Mac, and mobile PDF apps.
- Select your PDF, drag and drop a file onto the upload area, or click Browse to open the file picker. Files up to 100 MB are accepted.
- Set a password, type your chosen password. A strength indicator shows how secure it is. Re-enter it in the confirm field to avoid typos.
- Click Protect PDF, the file is processed entirely in your browser using AES-256 encryption. A progress bar tracks the operation.
- Download the protected file, click Download to save the password-protected PDF. The content is identical to the original, only a password is now required to open it. No watermark is added.
How AES-256 PDF encryption works
AES-256 is the strongest encryption standard available in the PDF format. When you set a password, the tool derives two cryptographic keys from it using SHA-256 and uses them to encrypt every content stream inside the PDF, text, images, fonts, annotations. The only way to read the protected file is to enter the correct password, which unlocks the keys and allows the viewer to decrypt the content in real time. The process runs in the background so the page stays responsive. Your password is never transmitted, it exists only in your browser's memory for the duration of the operation and is gone when you close the tab. If you need to reduce the file size before protecting it, try the PDF Compressor first.
What this protects against
This tool adds an open password, which means the protected PDF should not display until the correct password is entered. It is designed for private sharing, email attachments, client documents and personal records. It is not a full document rights-management system: once someone knows the password and opens the file, their PDF viewer may still allow printing, copying, screenshots or re-saving depending on the app they use.
Frequently asked questions
Is my PDF uploaded to a server?
No. Your PDF file never leaves your device. The password is applied entirely inside your browser using the AES-256 encryption standard. No file data is sent to PureTools servers or any third party. You can disconnect from the internet after the page loads and the tool will still work, your document stays completely private. Your data is never used to train AI models or improve machine learning systems.
What type of encryption does this tool use?
The tool uses AES-256 encryption, the same standard used by banks, governments and security professionals worldwide. Specifically, it applies the PDF Standard Security Handler Revision 5 (V=5, R=5) as defined in the PDF specification. This is the strongest encryption level available in the PDF format and is supported by modern PDF viewers including Adobe Acrobat, Chrome, Firefox, Safari and Preview on Mac.
Will the password work in all PDF viewers?
It should work in modern PDF viewers because AES-256 encryption is part of the official PDF standard. Adobe Acrobat Reader, Chrome, Edge, Firefox, Preview on Mac, Foxit Reader and other current applications should ask for the password before showing the document. If a very old viewer fails, open the file with an updated reader instead of weakening the encryption.
Is there a file size limit?
Yes, each PDF must be 100 MB or smaller. This limit protects your device memory since the tool holds both the original and the encrypted file in memory at the same time during processing. Most PDFs, including lengthy reports, slide decks, contracts and scanned documents, fall well under this limit. No data is saved to your device by this tool; everything is cleared when you close the tab.
What happens if I forget the password?
There is no way to recover the password or open the file without it, that is the point of encryption. AES-256 is designed so that even with modern computing power, a brute-force attack on a strong password is not feasible. Choose a password you will remember, or save it in a trusted password manager before protecting the file. PureTools does not store your password and cannot help you recover it.
Can I protect a PDF that already has a password?
No. If a PDF is already password-protected, this tool will show an error and stop. You must first remove the existing password using a dedicated tool, then add a new password here. Attempting to double-encrypt a PDF is not supported by the PDF standard and would produce a file that most viewers cannot open.
Does the tool add a watermark to the protected PDF?
No. The output file is identical in content to the original, the same pages, text, images, fonts and formatting, with the only difference being that a password is now required to open it. No watermark, no branding and no visible changes are made to the document content or page layout.
Does this stop copying, printing or screenshots?
No password-protected PDF can reliably stop screenshots, and copy or print restrictions are often treated as viewer preferences rather than absolute security. This tool focuses on the most important protection: requiring a password before the document opens. After someone enters the correct password, their PDF app may still allow printing, copying, exporting or screen capture. For confidential files, share the password through a separate channel and send the PDF only to people who should be able to read it.
Is my data erased when I close the tab?
Yes. Your PDF file and the password you enter are held only in your browser's memory for the duration of the operation and are automatically cleared when you close the tab. The tool does not use cookies or any form of persistent storage for your document or password. Closing the tab clears everything instantly, no trace of your file remains on the device.
How strong should my password be?
The tool displays a strength indicator as you type. A strong PDF password should be at least 12 characters and combine uppercase letters, lowercase letters, numbers and symbols. Avoid common words, names or dates. The strength meter turns green when your password reaches a good level. A strong password is the only thing standing between your document and anyone who gets the file, so it is worth taking a moment to choose a good one.