What Protect PDF does
Protect PDF encrypts a document with AES-256 so that it cannot be opened without a password, and optionally restricts what a reader who does open it can do — print, copy text, edit or fill forms. The encryption is applied in your browser; neither the file nor the password is sent anywhere. Use it before emailing a payslip, a contract, medical records, exam papers or anything else that should not be readable by whoever happens to see the attachment.
Two passwords, two jobs
| Password | What it controls | Who gets it |
|---|---|---|
| Open password (user password) | Whether the file can be opened at all | Everyone who should read the document |
| Owner password (permissions password) | Whether the restrictions (no printing, no copying) can be lifted | You — keep it private |
If you leave the owner password blank, the open password is used for both, which is fine for a document you simply want locked. Set a different owner password when you want readers to open the file but not to print or copy it.
Permissions explained
- Printing: allow full quality, low resolution only (150 dpi, discourages reprinting), or none.
- Copying: whether text and images can be selected and copied out. Screen readers keep access to the text regardless, as accessibility requires.
- Editing, annotating, form filling: whether the document can be changed, commented on or have its fields filled.
Restrictions are enforced by well-behaved viewers (Acrobat, Preview, browsers). They are a policy signal, not a hard barrier: anyone who knows the open password can rebuild the file with the Unlock PDF tool and drop the restrictions. For real confidentiality, the open password is what matters — and a strong one.
Choosing a password
- AES-256 is only as strong as the password. A 6-character word falls to a brute-force attack in minutes; a 12-character mix of words, digits and symbols does not.
- Use the Password Generator on this site for a random one, and send it to the recipient by a different channel than the file (a text message, a call).
- There is no recovery. If the password is lost, the content is gone — keep an unencrypted copy somewhere safe.
What changes in the file
- Every content stream, image and font is encrypted; the page structure remains visible to viewers so they can prompt for the password.
- Metadata (title, author) is encrypted too.
- File size grows by a few hundred bytes.
- Existing digital signatures are invalidated, since the bytes change. Sign after protecting, not before.