Protect PDF

A contract, payslip, medical report or ID scan often has to travel by email or WhatsApp. A password turns that PDF into a file only the intended reader can open — as long as the encryption is real. Plenty of free “protect PDF” tools only set a flag that some readers ignore, or send your document and its password to a server.

This tool encrypts the PDF with the standard PDF security handler: AES-256 (PDF 2.0 / Acrobat X and later) or AES-128 for older readers. The work is done by QPDF, a long-established open-source PDF library, compiled to WebAssembly so it runs inside your browser tab. Neither the file nor the password is uploaded.

You set an open password (needed to view the file) and choose whether readers may print, copy text and images, or edit and fill forms. A separate permissions password controls those restrictions; leave it empty and a random one is generated.

After protection, any standard reader — Adobe Acrobat, Chrome and Edge's built-in viewers, macOS Preview, Foxit, mobile PDF apps — asks for the password before showing a single page.

How It Works

1. Choose the PDF — up to 200 MB. The file is read into the page's memory; nothing is sent over the network.
2. Set passwords and permissions — type the open password twice (minimum four characters), optionally a permissions password, pick AES-256 or AES-128, and tick which actions are allowed.
3. Encrypt with QPDF — QPDF rewrites the file with every string and stream encrypted using a key derived from your password, and records the permission flags. Download the protected copy; your original is untouched.

Compatibility & Support

Supported Input → Output Formats

• Input: any standard PDF (PDF 1.0–2.0), including scanned and form PDFs
• Output: encrypted PDF — AES-256 (revision 6) or AES-128 (revision 4)
• Permissions: printing, copying text/images, editing/comments/form filling — each allowed or blocked

Unsupported Formats

A PDF that is already encrypted must be unlocked first with Unlock PDF (you need its password). Older RC4 encryption is deliberately not offered because it is considered weak. Permission restrictions are honoured by mainstream readers, but they are a policy flag, not a technical barrier once the file is open — use a strong open password for anything truly confidential.

File Size Limits

One PDF at a time, up to 200 MB. QPDF (the engine) is downloaded once, about 1.4 MB, and then cached by your browser. Very large files need free memory roughly three times their size while processing, which desktop browsers handle easily.

Who Should Use This Tool?

• Students: A student emailing a scanned passport and transcript to a university admissions office protects the PDF and sends the password by SMS.
• Freelancers & Designers: A designer shares a final proposal with printing and copying disabled so the concept can be reviewed but not lifted.
• Office Professionals: An HR officer sends salary slips as individually protected PDFs, each opened with the employee's own code.
• Developers: A developer checks how their app handles AES-256 encrypted PDFs by generating test files with known passwords.

Why This Tool Beats the Alternatives

• Genuine encryption, not just a “protected” label that some readers ignore.
• Your password is never sent to a server, so it can't be logged or leaked there.
• Modern AES only — no weak RC4 option.
• Free, no account, no watermark on your document.
• Clear explanation of what permissions can and can't enforce.

Pro Tips

• Send the password through a different channel from the file — PDF by email, password by SMS or a phone call.
• Use a passphrase of four or more words; AES-256 is only as strong as the password protecting it.
• Keep an unprotected original in a safe place. If the password is lost, nobody (including us) can recover the file.

Choose your PDF above, set a password, and download a properly encrypted copy.