Password protect PDF files with AES-256 encryption
Password protect PDF files with AES-256. The owner password is required. It is the password that removes the restrictions later. The user password is optional. Leave it empty and the file can open without a prompt, with the permission flags still set. Those flags are advisory in some viewers.
Loading tool…
or drop / paste
How to password protect PDF files
- Add one PDF. If it is already encrypted, type the password you already know so this page can open it before setting a new one.
- Type an owner password. The field is required. This is the password you will need later to lift the restrictions.
- Type a user password if opening the file should prompt. Leave it empty if the file should open and the permission flags should still be set.
- Set printing to high resolution, low resolution, or not allowed. Set the toggles for copying, modifying, annotating, form filling, and accessibility extraction. Form filling and accessibility extraction start on. The others start off.
- Press Protect PDF and download the file. Store the owner password somewhere you control. This page cannot show it to you later.
Protect PDF options explained
Encryption is AES-256. That part is the lock on the bytes. The printing and toggle settings are permission flags inside that encryption. Some viewers treat those flags as optional, especially when no user password was set and the file opens without a prompt.
An empty user password means there is no open prompt. The owner password still controls the flags. The page warns about that case. A viewer that ignores flags can still print or copy. Do not describe the toggles as a guarantee.
Owner password cannot be blank. If you only wanted a prompt when the file opens, you still set an owner password, and you set the user password to the prompt you want people to type. They are allowed to be different.
Owner password and user password
The owner password is what you keep. Unlock PDF, and any later edit on this site, needs a password that actually opens the file. If you set a user password, viewers ask for it to open. If you did not, the file opens and the flags are the only restriction, and only in viewers that honour them.
Forgetting the owner password is final on this site. There is no recovery, no hint, and no reset. Unlock PDF will not guess. Write the password down before you close the tab. The password is not saved with the page.
The new file’s producer line is Upload Nothing (uploadnothing.com). Encryption does not remove pages or flatten fields. If you need the form answers burned in before you lock editing, run Flatten PDF first. XFA forms are rejected by that tool.
What the flags are worth
Printing can be high resolution, low resolution, or not allowed. Copying, modifying, and annotating default to off. Form filling and accessibility extraction default to on, so a reader can often still fill a field and a screen reader can still extract text, unless you turn those off.
A viewer that treats the flags as advisory will let someone copy text anyway. The AES-256 encryption is still real. The honest claim is: a user password stops casual opening, and the flags ask cooperating viewers to limit what they offer. They are not a technical barrier in every reader.
Limits, formats and output
| Accepted input | |
|---|---|
| Files per batch | 1 |
| Soft size warning | 200 MB or 1,000 pages |
| Hard stop | 500 MB total in memory |
| Output | PDF, or a ZIP when there is more than one file |
| Account | None. The tool runs in this tab. |
Your file never leaves your device
Your PDF is encrypted by a script running in this tab. The work runs in a Web Worker in this tab, using WebAssembly for the heavy parts, and the result comes back as a local blob. This site does not upload the file, store it, or log its name.
To verify: load the page, turn on airplane mode, and drop the file again. It still finishes. Or open DevTools, choose Network, and watch the run: there is no upload. The architecture is described on How it works.
Frequently asked questions
What happens if I leave the user password empty?
The file opens without a password prompt. The permission flags are still written. Some viewers treat those flags as optional, so a person who can open the file may still print or copy. Set a user password when you want an open prompt. The owner password is required either way.
Which password removes the restrictions?
The owner password. Keep it. The user password, when you set one, is what a viewer asks for to open the file. Unlock PDF accepts the user or owner password you already know and copies the pages into a new file with no encryption. It does not recover a password you have lost.
Is AES-256 the whole protection?
AES-256 encrypts the file. The checkboxes are permission flags, and they are advisory in some viewers. Say that when you hand the file to someone. A determined reader with a viewer that ignores flags is not stopped by a copying toggle once the file is open.
Can I prevent printing?
You can set Printing to Not allowed, or to low resolution. Cooperating viewers should follow that. Viewers that ignore permission flags may still print. There is no separate setting that physically removes the page content.
Do you store the password?
No. It is used for this job in the tab and it is not written into an account, because there is no account. If you lose it, this site cannot email it back. The download is the only copy of the protected file this page creates.
Should I flatten the form first?
If the answers must not stay editable, yes. Flatten PDF burns the field appearances into the page and rejects XFA. Then protect the flat file. Protection alone leaves fields editable when form filling is allowed, and that toggle starts on.
Last updated 2026-09-26. By Tam.