PDF Password Protect

The tool parses the PDF in your browser, attaches an encryption dictionary, and re-serialises the file. Both the file contents and the object tree are encrypted with AES — any reader opening the file must supply the password before it will decode the pages. Restriction flags (no printing, no copying) are stored inside the encryption dictionary too.

Example

Input:  contract-draft.pdf — 280 KB
Action: set user password "H7-fw2pQ!ax9" + deny printing
Output: contract-draft-protected.pdf — 281 KB
        opens in Acrobat / Preview only with the password;
        print button is greyed out

Common errors and pitfalls

A few common mistakes turn a protected PDF into no protection at all, or lock you out of your own file. Avoid these.

• Setting restrictions without an owner password. Restriction flags only apply if an owner password is set — if you leave it blank, the flags are advisory and trivially removable. Set an owner password whenever restrictions actually matter.
• Using a weak password. PDF encryption is only as strong as the password. Short, predictable passwords fall to offline brute force in minutes. Use a 16+ character passphrase for anything valuable.
• Confusing user and owner passwords. User password = open document. Owner password = bypass restrictions. They can be the same string; many people leave the owner password blank and only set a user password.
• Encrypting an already-encrypted PDF. The tool will read the existing encryption (owner password restrictions only) and re-encrypt. If the input has a user password, unlock it first elsewhere.
• Treating restriction flags as a security boundary. Every mainstream PDF reader honours them, but any off-the-shelf tool (including /pdf-unlock on this site) can strip them. They are a speed bump, not a lock.

Owner password vs user password — what is the difference?

The user password is required to open and view the document — without it, the PDF cannot be read at all. The owner password is required to remove restrictions (printing, copying, editing) from an already-open document. Many PDFs set only an owner password so anyone can read the file but only the owner can print or copy from it. You can set either or both.

What password strength should I use?

PDF encryption is as strong as the password you pick. A short password (8 characters, lowercase) is crackable on a laptop in minutes; a 16+ character passphrase with mixed case, digits, and symbols is secure against casual attackers. PDF encryption is not suitable for classified or regulated data — use a proper encrypted archive (e.g. age, 7-Zip AES-256) for that.

Can I apply one password to many PDFs at once?

Yes. Drop any number of PDFs; each is encrypted with the same password and permissions you entered. Each file is processed in turn; download individually or grab the whole batch as a ZIP.

Which PDF viewers honour the restrictions I set?

Every mainstream PDF viewer — Acrobat Reader, Preview, Chrome, Firefox, Edge — honours user-password encryption (you cannot open the file without the password). Restriction flags (no printing, no copying) are honoured by well-behaved viewers but are ultimately advisory; a determined user with a different tool can strip them. Treat restriction flags as a speed bump, not a lock.

I protected a PDF and now I forgot the password — can the tool recover it?

No. Encryption is one-way: given only the encrypted file, there is no way to recover the password other than brute force. If you only applied an owner password, the sibling tool at /pdf-unlock can remove restrictions without knowing the password. If you set a user password (open-to-view) and forgot it, the file is effectively lost.

Does this tool support the latest PDF encryption standards?

Yes — the underlying library produces PDFs with AES-128 or AES-256 encryption (PDF 1.6 / 1.7), which every modern PDF viewer supports. It does not produce legacy RC4-40 encryption, which is considered broken.