One password, real AES-256, and nothing else to decide
Put a password on a PDF here and the file will not open without it. Not in Acrobat, not in a browser, not on a phone, not for anyone. That is the whole tool: one field, one password, and encryption the file actually carries rather than a note asking readers to behave.
What the encryption actually is
Every file gets AES-256, the strongest the PDF specification defines, and you can check it yourself rather than take our word for it. Open the locked file in a text editor and look at the encryption dictionary: it reads Filter Standard, R 6, V 5, Length 256, CFM AESV3. That combination is revision 6, the security handler introduced with PDF 2.0, and AESV3 is the 256-bit cipher. There is no weaker fallback and no "depending on the file".
Here is how that compares with the two best known tools in this category, taken from what each states on its own Protect PDF page.
| Tool | Encryption stated on its own page | Sells permission checkboxes? |
|---|---|---|
| This tool | AES-256, every file, every time | No |
| Smallpdf | 128-bit AES | No |
| iLovePDF | Not prominently stated | Yes, seven of them |
AES-128 is not broken and we are not pretending otherwise. But 256-bit keys are the current recommendation for documents that need to stay closed for years, they cost you nothing here, and always is a better answer than sometimes. And a tool that does not tell you what it applies is asking for trust it has not earned.
Why there are no permission checkboxes
Every other protect page offers a row of them: block printing, block copying, block editing. We deliberately do not, and the reason is worth two minutes of your time.
Those settings are not encryption. They are advisory flags written onto a file that opens freely for everyone, which means the decryption key is handed out with the document and honouring the flags is left to the reader's manners. Any unlock tool strips them in a fraction of a second without being asked for a password, including our own. Selling that as protection would be selling a lock with the key taped to it.
You do not have to take our word for that either. iLovePDF offers exactly those seven checkboxes under the Advanced tab of its Protect PDF page, and prints this underneath them: "Some applications not following PDF standards may not correctly apply these restrictions." That is the whole problem stated by the people selling it.
| The two locks a PDF offers | Does the file open? | Removable without the password? |
|---|---|---|
| Open password, what this tool applies | Not without the password | No. It is real AES-256 encryption |
| Permission flags, block printing and copying | Yes, freely, for everyone | Yes, by any unlock tool, instantly |
If you need people to read a document but not keep or reuse it, that is a rights management problem, and no honest PDF tool solves it with a checkbox.
It checks its own work
A lock that silently failed is worse than no lock, because you would send the file believing it was safe. After writing your file the tool reopens it and confirms three things: the file now demands a password, your password opens it, and the encryption reads back as genuine 256-bit AES. If any check fails, the job fails loudly instead of handing you something you merely believe is protected.
Changing a password on a file that is already locked
Same request, no second trip. Add the current password on the file card and type the new one in the password field. The file comes back knowing only the new password, and the old one is gone. A set of files that share one old password all change together.
What happens to your password and your files
Your password encrypts the file and is then dropped. It is never written into the job record, the thing your browser polls while the work runs; that record stores only a yes or no that a password was set. Your finished file is deleted from the server an hour after it is ready, and the job record an hour after that so a late download gets a clear expired message instead of a mystery. There is no account, so there is nothing tying a file to a person, and nothing is watermarked.
If you forget the password
Then the file cannot be opened, by you, by us, or by anyone. AES-256 has no backdoor and no recovery route, and our own Unlock tool will ask you for this exact password rather than guess at it. So store the password somewhere you will find it again, and keep your original unlocked copy: this tool hands you a locked copy and never touches the file you uploaded.
What you get
- AES-256 on every file, verifiable in the encryption dictionary of the file itself
- One password field and no checkboxes that do not hold
- The output reopened and checked before you get it, or the job fails loudly
- Password changing on an already locked file in the same request
- Your password used and dropped, never stored in any record
- No account, no watermark, and files deleted from the server an hour later
What's next?
Encrypted bytes do not compress, so run Compress PDF before you lock, not after. It is also worth clearing author names and GPS traces with Remove PDF Metadata first, since a locked file still carries them. And if you have the password and want it gone, Unlock PDF removes it in one pass.