Password protect a PDF
Lock a PDF with an open password and AES-256 encryption before you email or share it. Everything happens in this browser tab — your file and password never touch our servers.
How to password protect a PDF
- Choose the PDF. Drop it on the box above or click to browse. It is read into this tab's memory only.
- Type an open password twice. Use at least 8 characters; a short phrase like
maple-truck-41-lanternis both strong and easy to read out over the phone. - Optional: set permissions. Untick printing, copying or editing if recipients should only read the file. Add a separate permissions password if you want to change those rules later.
- Click Protect & download. A copy named
yourfile-protected.pdfdownloads. Your original file is untouched. - Send the password separately. Text or call it — never put it in the same email as the attachment.
When to protect a PDF
Password protection is the simplest way to meet "encrypt sensitive attachments" rules that many employers, accountants and schools follow. Typical examples:
- Emailing a tax return, W-2 or 1099 to your CPA.
- Sending a signed offer letter or pay stub to a landlord or lender.
- Sharing medical records, IEP documents or report cards with family.
- Distributing a paid course workbook where you want to discourage copying.
What we do with your file
Nothing — it never reaches us. The page loads an open-source PDF library (pdf-lib), encrypts the document inside your browser, and hands the result back to you as a download. You can confirm this by disconnecting from the internet after the page loads: protecting a file still works, except the free-run counter can't be checked.
Frequently asked questions
How strong is the encryption?
By default SlatePDF uses AES-256, the strongest standard PDF encryption (PDF 2.0 / Acrobat X and later). With a long, unique password the file cannot practically be opened by guessing. You can switch to AES-128 if someone needs to open it in a very old reader.
Is my PDF or password sent to your server?
No. Encryption runs in your browser. The only thing the page tells our server is that one free protect run was used, so we can apply the daily limit. The file and the password never leave your device.
What happens if I forget the password?
We cannot recover it — we never see it. Keep an unprotected original in a safe place or store the password in a password manager before you send the protected copy.
What is the difference between the open password and permissions?
The open password is required to view the file at all. Permissions (printing, copying text, editing) are restrictions that standards-compliant readers like Acrobat, Preview and Chrome enforce for people who open the file with the open password. They are a courtesy lock, not strong security, so rely on the open password for confidentiality.
Will the protected PDF open on iPhone, Mac and Windows?
Yes. AES-256 protected PDFs open in Adobe Acrobat Reader, Apple Preview and Files, Chrome, Edge, Firefox and Microsoft Word, all of which prompt for the password.
How many files can I protect for free?
Without an account you can protect 3 files a day; a free account raises that to 10, combined across Protect and Unlock each. Pro removes the limit and raises the file size from 25 MB to 200 MB.