Protect PDF

To password protect a PDF, load it into the protector above. Type the password, type it again so a typo cannot lock you out, and choose Protect PDF. A copy downloads whose name ends in “-protected”. Opening that copy in Preview, Acrobat, Chrome or any other reader asks for the password before the first page appears. Phones and tablets work the same way: pick the file, type the password twice, and the download lands in the usual place. The original file on your device is left as it was.

1. Pick a PDF or drag it onto the protector. Anything up to 50 MB will open, as long as it is not already locked.
2. Type the password in both boxes. The eye button shows what you typed, which helps with a long password.
3. Choose Protect PDF. If the two boxes differ, nothing is written and you can correct them.
4. The copy saves with “-protected” on the end of its name. Send that file, and keep the original if you still want a copy that opens with no password.

The password this tool adds is an open password, also called a user password. It encrypts the contents of the PDF with AES-256, the strength current readers expect. Until that password is typed, a reader has no pages to show: not a thumbnail, not a line of text, not an embedded image. That is the lock people mean when they ask to password protect a PDF before emailing a contract, a tax form, or a scan of an identity document.

The same password is stored as the owner password, and every permission stays on. After the file opens, printing, copying text and editing are allowed. There is no second, secret password. If you can open the file, you can use it. Write the password down somewhere you can find it. zoopkit does not keep a copy, and a forgotten open password cannot be recovered from the file.

PDF has a second, weaker kind of lock. An owner password can ask readers to block printing, copying, editing or page changes, while the file still opens with no password at all. Those requests are not encryption. Many readers ignore them, and remove the password on this site removes them without asking for anything. Adding that kind of block here would look like protection and would not be. The protector therefore adds only the open password, and says so on the tool.

If a form or a portal has told you to stop people printing, an open password is the control that actually works: they cannot print a page they cannot open. Share the password with the people who should read the file, and with no one else.

A PDF that already asks for a password, or that already blocks printing and copying, is turned away. Putting another password on top of an existing lock makes it unclear which password opens the file, and a permissions-only lock is not something this tool should quietly replace. remove the password first. When you have the open password, the unlocker writes a plain copy; when the file only has restrictions, it writes that copy with no password at all. Protect that copy if you still want an open password on it.

AES-256 in a PDF stores the password as UTF-8, up to 127 bytes. A password of ordinary letters and numbers can be quite long inside that limit. Accented letters and many other characters take more than one byte, so a password that looks short can still be too long. The protector counts bytes and refuses anything past the limit before it writes a file.

A comma or an equals sign is also refused. The engine that writes the file takes its instructions as a list separated by commas, and an equals sign marks the end of an instruction name. Letting those characters through would make the password look like part of the instructions. Spaces are allowed. An empty password is not: a file that opens with a blank password is not protected.

A certificate signature is a seal over one exact file. Saving a protected copy produces a different file, so that seal no longer validates, even though the pages look the same. When the protector sees a signature, it says so after the download. Keep the original if a court, a client or a portal needs the signature to check out, and protect a separate copy for sending.

A password is only useful if it stays with you. The protector opens the PDF in your browser tab using MuPDF, a PDF engine compiled to run inside the page, so zoopkit receives neither the file nor the password. The password exists only while you are using the page and disappears when you open another file or close the tab. It is not written to storage on your device and it is not included in the usage record. The code is open source under the AGPL-3.0 license, linked from the bottom of the tool.

The protector handles one PDF of up to 50 MB. It adds an AES-256 open password and leaves printing, copying and editing allowed. It does not remove a password, and it does not guess one. Certificate encryption and rights-management systems that phone a server are outside what a password in the file can express, so those files should be handled by the software that created them. You never sign up, and nothing remains once the tab is closed.