Passwords and security

Opening a protected document

A PDF can be protected with two passwords:

• The password to open it (sometimes called the user password). Without it the document can’t be read.
• The password to change the restrictions (sometimes called the owner password). It opens the document too, and lifts the restrictions its author set.

When you open a protected document, Nixt PDF asks for a password in the This document is locked dialog. Either password works. See Opening a password-protected document for the steps.

• Passwords are checked on your computer, and are never sent anywhere or stored.
• Passwords are exact: capitals matter.
• The document stays unlocked while it is open, so its outline, form, text and every tool work normally. Close it and open it again, and it asks again.

Kinds of protection Nixt PDF opens

A document protected in a way Nixt PDF can’t open shows why, in a sentence starting Nixt PDF cannot open this document because — for example, because it uses a security handler that needs software from whoever issued the document. There is no Unlock button, because no password would work.

Working on a protected document

• Everything you add to a protected document — comments, form answers, stamps — is encrypted with the document’s own protection. Marking a document up never removes its protection.
• Commands that rewrite the whole document, such as redaction or Save pages as a PDF…, keep the protection too.
• Home › Properties… shows the protection under Protection, such as AES-256 (revision 6), and adds , opened as owner when you used the password to change the restrictions.

Protecting a document with a password

1. On the Protect tab, click Password… (or choose More › Protect with a password…).
2. In the Protect with a password dialog, type a password in Password to open the document.
3. Type it again in Type it again. These do not match is shown until the two are the same.
4. Optionally, type a different password in Password to change the restrictions (optional). Left empty, the password above does both.
5. Under What readers may do, turn off anything readers shouldn’t do. See Restrictions.
6. Click Protect.

The message says Protected with AES-256. Save the document to write it to disk.

Protect is dimmed until the two copies of the password match and there is something to do: a password, or at least one restriction.

What happens:

• The document is encrypted with AES-256, the strongest protection PDF defines.
• The whole document is rewritten. Every earlier revision goes with it, so the pages as they were before can’t be recovered from the file.
• The undo history is cleared, so this can’t be undone. Remove the password instead if you change your mind.
• Digital signatures in the document stop matching.

A document anyone can open, with restrictions

Leave Password to open the document and Type it again empty, type a password in Password to change the restrictions (optional), and turn off the restrictions you want. The document opens for anybody, and still records what its author asked readers not to do.

Changing the password

On a protected document, the command reads Change password… on the ribbon and Change the password… in the More menu. It opens the same dialog, titled Change the password, and replaces the protection with the new passwords and restrictions.

Restrictions

The four switches under What readers may do are all on to start with:

As the dialog says: These are recorded in the file and shown by readers that choose to honour them. Nothing enforces them — a reader that has decrypted a document can do anything with it, including this one.

How Nixt PDF treats restrictions on documents you open:

• Printing: a document set not to be printed isn’t printed. The Print dialog says This document was set not to be printed — unless you opened it with the password to change the restrictions.
• Everything else is shown in Home › Properties… under Author asks you not to.

Removing a password

1. Open the document with its password.
2. On the Protect tab, click Remove the password (or choose More › Remove the password). It’s dimmed on a document that isn’t protected.
3. In the Remove the password? dialog, read Anybody who has the file will be able to open it. The document is rewritten, so the protected version cannot be recovered from it, and this cannot be undone.
4. Click Remove it.

The message says The password is off. Save the document to write it to disk.

Either password can be used to open the document before removing its protection.

What Nixt PDF never does with a document

• It never runs scripts a document contains.
• It never follows a link on its own. Web and email links ask first, and links that would open a file or start a program are refused. See Following links.
• It never opens attached files. They can only be saved. See Attached files.
• It never sends a document anywhere.

To see what a document is carrying — scripts, actions, attachments, metadata, hidden layers — and take it out, see Hidden content.

Messages