How to add a password
- Add one or more PDFs.
- Enter the password that will be needed to open them, and confirm it. Use at least 6 characters; longer is better.
- Optionally set a separate owner password and choose whether printing is allowed.
- Click Add password and download.
How the protection works
The tool encrypts the document's contents with AES-256, the strongest encryption the PDF standard defines, using a key derived from your password. Without the password the file's text and images are unreadable; a viewer asks for the password before showing anything. The encryption happens in your browser, so the unencrypted document and the password never leave your device.
The strength of the protection is the strength of the password. A short or common password can be guessed by software that tries millions of passwords. Use a long passphrase (four or five random words, or a password-manager-generated string) and do not reuse one from another account.
Open password and owner password
- The open password (user password) is needed to view the document at all.
- The owner password controls permissions, such as printing, copying text and editing. Viewers that respect permissions enforce them for anyone who opened the file with the open password. Permissions are a polite request rather than strong security: they are enforced by viewer software, not by the encryption.
If you leave the owner password blank, it is set to the open password.
Sending the password
Never send the password in the same email as the file. Use a different channel, such as a text message, a phone call or a password manager's sharing feature, so that someone who intercepts one does not get both.
When not to encrypt
- Upload portals. Many government and employer portals cannot read encrypted PDFs and reject them; ImmiAccount is commonly reported to be one. Upload the original.
- Archiving. An encrypted archive copy is only as available as its password. Archive the original somewhere secure instead.
- Accessibility. Some assistive technology struggles with protected files.
Removing the password later
If you know the password, Remove PDF password decrypts the file and saves an unprotected copy, also in your browser.
Choosing a password
A password protects a PDF only as well as it resists guessing. Four or five random words ("lantern-orbit-pepper-quarry") are long, easy to type and hard to guess. Avoid dates of birth, names, and anything printed in the document itself. A password manager can generate and store one, and share it securely with the recipient.
What encryption does not do
Once someone opens the file with the password, they can save, print (if allowed) and forward its contents. Encryption controls who can open the file, not what an authorised reader does next. For documents you also need to mark, combine a password with a watermark, and send the file only to people who should have it.
Several files at once
Add several PDFs and each is encrypted with the same password. That suits sending a set of documents to one recipient; tell them the one password through a separate channel.
Encryption strength
PDF encryption has improved over the years. Old 40-bit and 128-bit RC4 encryption can be broken quickly and should not be used. AES-128 is sound, and AES-256 is the current standard; this tool always uses AES-256. If someone needs to open the file in very old software that cannot read AES-256, they should update their reader rather than you weakening the encryption.
Sending to an accountant or lawyer
Professionals often ask clients to email documents. A password-protected PDF, with the password sent by text message or phone, is a simple step up from a plain attachment. Agree the password format once, so you are not inventing a new one each time, but do not use the same password you use for any account.
Opening protected files
Recipients open the file as usual and are asked for the password. Browsers, Adobe Acrobat and Reader, macOS Preview, and the built-in viewers on iPhone and Android all support AES-256-protected PDFs. If someone reports they cannot open it, check they are typing the password exactly, including upper and lower case.
Encryption runs in your browser tab, and the password is never stored or sent anywhere.
Privacy: the file stays on your device
Online PDF services upload your document to their servers, process it there and keep it for a while. This tool does the work in your browser. The file is read into the page's memory, processed by open-source libraries (pdf-lib for editing and pdf.js for rendering) in a background worker, and the result is offered back as a download. Nothing is sent anywhere, there is no account, and closing the tab discards everything. You can check it: open your browser's developer tools, watch the Network tab while you run the tool, and you will see no upload. After the page has loaded once it also works offline.