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Passwords

How to password protect a PDF

By DeckleUpdated

To password protect a PDF, open Password protect PDF, choose your file, type a password of at least six characters in Password and again in Confirm password, then choose Protect this PDF. Deckle saves an AES-256 encrypted copy that asks for the password every time it is opened. Your original file stays unprotected and unchanged.

Password protect PDF

Protect access, then check the saved copy

Source PDF

Keep a separate original

Protected output

Freshly reopen it to check the opening password

An opening password does not redact page content

Conceptual workflow · password protection controls access to content that remains in the document.

How to password protect a PDF with Deckle

  1. Open Password protect PDF and choose your PDF, or drop it onto the page. A preview of the first page appears so you can confirm it is the right file.
  2. Type the new password in Password. The hint under the field reads "At least 6 characters."
  3. Type it again in Confirm password. If the two entries differ, "The two passwords do not match." appears under the field as you type.
  4. Choose Protect this PDF. Until both fields are valid, the button stays disabled and says what is missing, such as "Type the same password in both fields."
  5. Download the copy, which has "(protected)" added to its name.
  6. Open the download in your PDF reader and enter the password to check that every page appears.

The result screen reads "Password required to open" with "AES-256 protection added". Before it appears, Deckle tests the new file: it must refuse an empty password and open with the one you set.

What the protected copy contains

The new PDF has the same pages, page sizes and text as the original. Only the encryption is new.

  • One password opens the file. Deckle sets it as the open password and uses the same value as the owner password.
  • No permission settings. Deckle has no option to block printing or copying. Because the open password is also the owner password, entering it gives full access.
  • Producer is set to Deckle. If you want the author, title or other properties gone, run Remove PDF metadata before you protect the file. Once it is locked, other tools need it unlocked again first.

Example: a 12-page tenancy agreement called lease.pdf becomes lease (protected).pdf. It still has 12 pages, and every reader that supports PDF encryption asks for the password before showing page 1.

Choose the password

Six characters is the minimum the form accepts, not a target. A longer password is much harder to guess. A passphrase of four or five unrelated words, or a random string from a password manager, works better than a name, a date or a word from the document itself. How to choose a strong password for a PDF covers this in more detail.

Write the password down in a password manager before you send the file. The note under the fields says it plainly: "Save this password somewhere safe. You cannot recover it." Deckle does not keep a copy, and there is no reset link.

The PDF already has a password

Password protect PDF needs a file without a password. If your PDF already asks for one, or carries restrictions, unlock it first with Unlock PDF using the current password, then protect the unlocked copy with the new password. The full sequence is in how to change the password on a PDF.

If the PDF is digitally signed, adding encryption rewrites the file, and the signature will not validate on the protected copy. Keep the signed original and protect a copy only if the recipient does not need to check the signature.

Tips

  • Send the file and the password separately. Email the PDF and give the password by phone or in a different app, so one intercepted message does not open it. See how to share a password-protected PDF.
  • Protect the final version. Merge, reorder and clean the document before you lock it, because every later change needs an unlock first.
  • Test in a fresh reader window. Close any copy that is already open, then open the download. It should ask for the password straight away.
  • Delete the unprotected original if it should not stay around. Deckle never changes it, so it remains wherever you saved it.

Other ways to password protect a PDF

  • Preview on a Mac. Choose File > Export, click Permissions, select Require Password To Open Document and enter the password twice. Enter an Owner Password as well, leave unselected any action that should need it, then click Apply and Save. Give the export a new name if you want to keep the original unprotected.
  • Adobe Acrobat Pro. Choose All tools > Protect a PDF to add an open password, a permissions password or both. The free Acrobat Reader cannot add a password.

Frequently asked questions

Can I password protect a PDF without Adobe Acrobat?

Yes. Password protect PDF runs in your browser, so there is nothing to install. The file is encrypted on your device and is not uploaded.

How secure is AES-256 for a PDF?

AES-256 is the strongest encryption the PDF standard defines, and Deckle never writes the older RC4 method. The weak point is usually the password, so make it long and unique. See what AES-256 PDF encryption protects.

Can I stop people printing or copying the PDF?

Not with this tool. It sets one password that is needed to open the file. Once opened, the reader's own features apply. Preview and Acrobat can set permission restrictions if you need them.

What happens if I forget the password?

The protected copy cannot be opened without it, and Deckle cannot recover it. If you still have the unprotected original, protect it again with a new password.

Can I protect several PDFs at once?

No. Each run takes one file. Protect them one by one, or merge them first with Merge PDFs and protect the combined file.

Related tools

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