How to password-protect a PDF
- Drop one or more PDFs into the box above.
- Type the password that should be needed to open them, then type it again.
- Optionally open Restrict printing, copying or editing and tick what to block.
- Click Protect PDF. Each file is encrypted and checked, then ready to download as
…-protected.pdf.
The original file is not changed. Several files get the same password; download them one by one or together as a ZIP. If a file is already protected, the tool says so instead of encrypting it twice — remove the old password with Unlock PDF first if you want to set a new one.
Checked before you download
A protected file that quietly opens without a password is worse than no protection, because you believe it is safe. So after encrypting, the tool opens the result again with a different PDF reader from the one that encrypted it and runs two tests: the file must refuse to open without the password, and it must open with your password and show the same number of pages as the original. The outcome is written under the download button. If either test fails, you see a warning instead of a green tick.
What encryption hides — and what it doesn't
PDF encryption scrambles the text, images, links and document information such as the title and author. It does not scramble the file's skeleton — and in many PDFs that skeleton gives away more than people expect. We printed a two-page letter to PDF from Chrome, encrypted it with AES-256 in two ways and searched each result for readable details:
| Readable without the password | Standard encryption | This tool |
|---|---|---|
| Number of pages | Yes | No |
| Size of every page | Yes (both page boxes) | No |
| Names of the fonts used | Yes (Georgia, Georgia Bold) | No |
| Pixel size of each image | Yes | Yes |
| File size | 42.1 KB | 31.1 KB |
The difference comes from how the file is packed. Most PDFs saved from browsers and office programs keep each page's description as plain structure next to the encrypted content. Before encrypting, this tool packs those descriptions into compressed, encrypted sections, which also makes the file smaller. Image dimensions and the file size cannot be hidden by any PDF encryption; when your document contains images, the result tells you how many.
Open password vs. restrictions
The open password is real protection: without it, the content is encrypted with AES-256 and cannot be read. Restrictions on printing, copying and editing are a different thing. They are a note inside the file that PDF apps are asked to respect. Adobe Reader and most viewers do, but anyone who can open the file can strip them with free software, including our own Unlock PDF. Use them to discourage casual copying of a shared handout, not to protect secrets.
Restrictions are tied to a second, permissions password. It has to differ from the open password; if the two are the same, whoever opens the file also has the right to lift the restrictions. Leave the field empty and a random 20-character one is created and shown with the result, so you can lift the restrictions later if you need to.
Choosing a password
Once someone has the file, nothing limits how many passwords they can try. AES-256 does
not help if the password is summer2026. Three or four unrelated words, or 12 or
more mixed characters, keep the file out of reach. Send the password by a different route
from the file — a text message or a phone call rather than the same email — and
keep it in a password manager, because a forgotten PDF password cannot be recovered.
Digitally signed PDFs are a special case: adding a password rewrites the file, and signature checkers then report the signature as broken. The tool warns you when a file carries a digital signature. To fill or sign a document before protecting it, use Fill PDF Form or Sign PDF; to make it small enough to email, compress it first, because an encrypted file cannot be compressed afterwards. More tools are on the PDF tools page.