About Protect PDF
Setting an open password encrypts the contents of a PDF. Anyone who tries to view it, in any reader, is asked for the password first, and without it the pages are just scrambled data. That is worth doing for tax returns, payslips, medical letters, signed agreements and anything else you are about to email or keep somewhere you don’t fully control.
This tool encrypts with AES-256, the method specified in the current PDF standard, ISO 32000-2 (PDF 2.0). The protected file opens in Adobe Acrobat Reader X and later, in the PDF viewers built into current browsers, in macOS Preview and in most modern reader apps. Very old readers that predate AES-256 may refuse it, so if a recipient uses unusually dated software, send them a test file first.
Doing the encryption locally has a real advantage. To lock a document on a remote server, you first have to upload it unlocked, which is exactly the copy you are trying to keep private. Here the work happens inside your browser tab: the original PDF and the password you type stay on your device, and only the encrypted result lands in your downloads folder.
How to use Protect PDF
- Load the PDF to lockDrop it onto the tool or browse for it. If the file already has a password, remove that with Unlock PDF first, then come back here to set a new one.
- Enter the password twice, set permissionsType the password and repeat it to rule out a typo. Printing and copying text are allowed by default while editing is not; flip any of the three switches to suit the person receiving the file.
- Save and test the encrypted copyDownload the protected PDF and open it once in your usual reader to confirm the password works, before you delete the original or send the copy on.
When people use it
Emailing tax papers to an accountant
Encrypt the return before attaching it, then share the password by phone or text message. A misaddressed or intercepted email then carries a file that nobody else can open.
Keeping records in cloud storage
Scanned passports, insurance policies and statements in a synced folder gain a second layer of protection: even if the account is accessed, each document still demands its password.
Handing over a final report
Leave editing switched off and printing on. The client can read and print the report, while PDF editors that respect the permission settings decline to change it.
The open password and the three permission switches
The open password is required; it is what actually encrypts the document. The permission switches add rules about what a reader may do once the file is open:
| Switch | Default | When on, readers may |
|---|---|---|
| Allow printing | On | Print the document |
| Allow copying text | On | Select text and images and copy them elsewhere |
| Allow editing | Off | Change pages and add or modify content |
Permissions are instructions to software. Readers that follow the PDF standard, Acrobat among them, enforce them, but some apps ignore them, and anyone who knows the password can always read the content. The encryption keeps out people without the password; the switches only steer the behavior of people who have it.
Choosing a password that holds up
- Length beats tricks. A phrase of four or more unrelated words is easier to remember than a short jumble of symbols and much harder to guess.
- Keep it unique. Don’t reuse the password from your email, bank or any other account.
- Use a separate channel. Send the password by text or phone call, never in the same email as the attachment.
- Write it down safely. A password manager is the best place for it.
AES-256 itself is a strong, widely trusted cipher. In practice the weak point is the password: a short or common one can be found by simply trying likely candidates.
A lost password is gone for good
pd00 never sees, stores or transmits the password, so there is no reset link and no recovery service. Unlock PDF works only when you supply the correct password. Before encrypting anything important, store the password somewhere reliable or keep an unprotected original in a safe place.
What changes inside the file
Text, images, fonts, links, bookmarks and form fields stay exactly as they were, and nothing is re-rendered, so after the password is entered the pages look identical to the original. The title, author and other document properties carry over. The file size stays close to the original. Note that the file name itself is not encrypted, so avoid putting sensitive details in it, and remember that once a recipient opens the file they can save or print it according to the permissions you chose.
The document and the password stay in this browser tab while it encrypts. Follow the verification steps to confirm that nothing is uploaded.