Payslips, medical reports, tax documents and bank statements are routinely sent by email, and an email can be forwarded, misdirected or read from a stolen phone. Putting a password on the PDF means that whoever ends up with the file also needs the password to open it. It is one of the simplest precautions available, and you almost certainly already have software that does it for free.
This site does not add passwords itself, because the browser library it is built on cannot write PDF encryption. It would rather send you to tools that do it properly than offer a weak version. Here they are.
The two kinds of PDF password
A PDF can carry two different passwords, and confusing them is the most common mistake.
The open password (sometimes called the user or document open password) encrypts the file. Without it, the file cannot be opened or read at all. This is the one that protects the contents.
The permissions password (owner password) leaves the file readable by anyone but asks PDF readers to block printing, copying or editing. Many readers and tools simply ignore these restrictions. Treat a permissions password as a polite request, not protection.
If the goal is privacy, set an open password.
Microsoft Word
If the document started in Word, protect it as you export. Choose File, Save As, pick PDF as the file type, then press Options and tick Encrypt the document with a password. Word asks for the password when you save. The exact wording varies slightly between versions, and the option is in the Windows version of Word.
LibreOffice, free on any computer
LibreOffice can protect a PDF made from any document it opens. Choose File, Export As, Export as PDF, go to the Security tab and press Set Passwords. Enter an open password, and optionally a permissions password. LibreOffice can also open an existing PDF in its Draw program and export it again with a password, although complex layouts may shift slightly when you do.
macOS Preview
On a Mac, open the PDF in Preview and choose File, Export. On older versions of macOS, tick Encrypt and enter the password twice; on newer ones, press Permissions and set a password required to open the document. It takes ten seconds and needs nothing installed.
Choosing and sending the password
A password is only as good as the way it travels. Sending the password in the same email as the file protects nothing: whoever has one has both. Send it by a different route: a text message, a phone call, or a message on a different app.
For documents you send to the same person often, agree a pattern in advance. Banks do this when they protect statements with something only the customer knows, such as part of their date of birth and account number. That is convenient, but guessable by anyone who knows those details, so for anything sensitive use a longer, unrelated password.
Length matters more than complexity. Four random ordinary words are far harder to guess than a short password full of symbols, and much easier to read out over the phone.
Before you encrypt
- Remove what does not need to be there. Encryption protects a file in transit, but the recipient sees everything. If they do not need your account numbers, redact them first.
- Check the hidden details. Author names and software details travel inside the file; PDF metadata shows and clears them.
- Do the merging and compressing first. Most tools, including the ones on this site, cannot work on an encrypted PDF, so finish the document, then protect it as the last step.
Lost the password to a PDF you made yourself? See how to remove a password from your own PDF.