Add password to PDF

Add password to PDF encrypts every file with 128-bit AES under revision 4 of the PDF standard security handler — V 4, R 4 and the AESV2 crypt filter, in the terms the specification uses. That choice is enforced rather than inherited: the source document's version header is normalised to 1.7 before encryption, because the library picks its algorithm from that header and older files would otherwise have quietly received 40-bit or 128-bit RC4, which is far weaker than the interface implies. After encrypting, the tool re-opens the security dictionary it just wrote and checks the version, revision, key length, crypt filter and permission bits; if any of them disagree with what you were shown, the download is cancelled rather than handing you a weaker file.

A user password is what a reader demands before it will open the document at all; an owner password only governs who may change the restrictions. A file with an owner password but no user password opens instantly for everybody and merely asks viewers to honour flags such as no printing — which is why such files are trivially stripped. This tool sets your password as both, so the document genuinely cannot be opened without it and there is no second password to manage. The consequence is worth stating plainly: whoever you give the password to can also remove the protection, because they hold the owner credential as well. If what you actually want is a file that anyone can open but nobody should edit, that is a different configuration from the one this tool produces.

The permission flags are a request to the viewer, not an enforced lock. They are stored in the encrypted document as a bit field, and compliant readers such as Acrobat, Preview and the built-in browser viewers do respect them: a file with copying unticked will grey out copy-and-paste. But nothing in the format prevents a non-compliant tool from ignoring the flags entirely once the password is known, and the tool card says exactly that beneath the checkboxes. Treat them as a deterrent that stops honest mistakes, not as a control that stops a determined recipient. The confidentiality comes from the encryption and from keeping the password secret. The panel above the button therefore reports which permissions remain allowed and names them, so what you are promising a recipient is never left implicit.

Revision 4 of the security handler can store only a 32-byte Latin-1 password, so anything longer or outside that character range is refused up front. A longer password would be silently truncated to its first 32 characters, meaning the file would not be protected by the password you thought you set; an emoji or a non-Latin script cannot be encoded at all. Rather than let either failure happen quietly, the field explains the reason as you type. Within those limits, length and unpredictability still matter — a 32-character passphrase of ordinary Latin letters, digits and punctuation is very strong, so take one from a password manager instead of shortening a familiar word.

No — a forgotten PDF password cannot be recovered, here or anywhere else. There is no recovery path, no backdoor and no copy of anything on our side, because the encryption happened in your browser and neither the file nor the password was ever transmitted. Remove PDF password can strip protection only when you supply the correct password; it does not guess and it does not crack. A well-chosen AES-128 password is not something a home computer works through in any useful timeframe, and that is precisely the property that makes the protection worth applying. Store the password in a password manager the moment you create it, and send it to your recipient over a different channel than the document itself. If the same document still exists somewhere in unencrypted form, re-encrypting that copy is far quicker than any attempt at recovery.

Add password to PDF is free, without a signup or a limit, and neither the document nor the password you type ever leaves your device. Encryption runs in the browser tab through @cantoo/pdf-lib, a maintained MIT-licensed fork of pdf-lib that adds AES password support; the file is read locally, encrypted locally and written straight to your downloads with no watermark of any kind. The password lives only in the page's memory while the tab is open and is discarded when you reset the tool or navigate away. That property is the reason to use a tool like this at all — a protection tool that uploaded your plaintext file first would defeat its own purpose.