How to Password-Protect a PDF Before You Email It
By the UtilityNest team · · 5 min read
Your accountant needs last year's tax return, three bank statements and a copy of your passport. You are about to attach them to an ordinary email, and you have a small, uncomfortable thought: this email will sit in two inboxes, maybe on a phone that gets lost, maybe forwarded to the wrong person by accident, for years.
A password on the PDF fixes most of that worry. Anyone who gets hold of the file without the password sees nothing but a password prompt. It takes about a minute and is free.
The short version: open Protect PDF, add the file, type a strong password twice (or click Generate), leave AES-256 selected and click Protect PDF. Then send the password by a different route than the file, such as a text message.
Step by step
- Open Protect PDF and add the PDF you want to lock.
- Type a password twice, or click Generate to create a strong one. A generated password is copied to your clipboard so you can paste it straight into a message.
- Keep AES-256 selected. Choose AES-128 only if the file has to open in very old PDF readers.
- Optional: switch on restrictions to block printing, copying or editing.
- Click Protect PDF and download the encrypted file.
The encryption happens in your browser, so the document is never uploaded, which is rather the point when the document is your tax return. After encrypting, the tool also re-opens the result to check that it cannot be opened without the password and opens correctly with it.
A worked example: sending documents to your accountant
Five files: a tax return, three bank statements and a passport scan.
- Combine them first with Merge PDF, so there is one file and one password instead of five.
- Protect the merged PDF, clicking Generate for the password. You get something like
violet-harbor-71-cactus, already on your clipboard. - Email the PDF. Text the password to the accountant's phone, or read it out on a call.
Anyone with the email, a forwarded copy or the lost laptop can open your passport and statements instantly.
Without the password the file shows only a prompt. The contents are encrypted with AES-256, not just hidden.
Never put the password in the same email as the file. If someone gets into that inbox, they get both. A text, a phone call or a different messaging app is far safer.
Choosing a password that actually protects
AES-256 is the strongest option in the PDF standard, but encryption is only as good as the password. A short or guessable one can be cracked by trying lots of guesses quickly.
- Use at least 12 characters. Three or four random words strung together are long, strong and easy to read out over the phone.
- Avoid birthdays, pet names and anything the recipient could guess from your social media.
- Store it in a password manager. There is no way to recover a forgotten PDF password, so also keep your original unprotected copy somewhere safe.
Open password versus restrictions
There are two different things a protected PDF can have:
- An open password. Needed to view the file at all. This is what actually protects the content.
- Restrictions (no printing, no copying, no editing). These are honored by Acrobat, Chrome and most viewers, but some software ignores them. They are good for discouraging casual copying, not for secrets.
If you set restrictions without an owner password, the tool creates a random one and shows it to you, so you can change the restrictions later. Save it.
Will the recipient be able to open it?
Yes. AES-256 protected PDFs open in Adobe Acrobat Reader X and later, Chrome, Edge, Firefox, macOS Preview, and the PDF viewers on iPhone and Android. They simply ask for the password first.
Other ways to add a password
Microsoft Word
If the document starts life in Word on Windows, choose File > Save As, pick PDF, click Options and tick Encrypt the document with a password.
Mac Preview
Preview's File > Export dialog can encrypt a PDF with a password; on recent macOS versions the setting sits under Permissions.
Adobe Acrobat Pro
The paid version has a Protect tool with the same kinds of options, if you already have a subscription.
When a password is not enough
A password protects the file in transit and at rest. It does not stop the recipient from sharing the decrypted contents once they have opened it. For very sensitive documents, check whether your accountant, lawyer or bank offers a secure client portal, which also keeps a record of who accessed what.
Locking a PDF on your phone
The same tool works in Safari on an iPhone or Chrome on Android. Tap the drop area and pick the PDF from Files, Drive or Downloads, set the password, and the protected copy saves back to your phone, ready to attach to an email. That is handy when the document came to you as a phone scan in the first place. If you are protecting several documents for the same person, it is kinder to merge them first so they only have to type one password.
Quick answers
Is my PDF uploaded to encrypt it?
No. Encryption is done by your browser and the file never leaves your device.
Can I remove the password later?
Yes, if you know it. Unlock PDF saves an unencrypted copy.
Can I stop people printing my PDF?
You can turn on a no-printing restriction, and most readers respect it. It is not enforceable in every program, so do not rely on it alone.