Password Protect a PDF
Put a password on a PDF before you send it. The file is encrypted with 256-bit AES and the password you choose both opens the document and controls printing, which is what people mean by protecting one. Write the password down before you download — there is no recovery, here or anywhere, and that is the point of encryption working properly.
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Add to Chrome — freeWhat it does
- 256-bit AES, not the breakable legacy option
- The password opens the file and controls printing
- The password is never stored or logged
- No watermark and no sign-up
How to use Protect PDF
- 1
Add the PDF
Drop the file in or choose it from your computer. The page count is read so you can confirm you picked the right document.
- 2
Choose a password, twice
The second field is not decoration — a mistyped password produces a file nobody can open, including you. The button stays disabled until both match.
- 3
Save it, and save the password
Download the protected copy and record the password somewhere before you close the tab. There is no way to recover it afterwards.
Encryption that is actually encryption
PDF has supported password protection since 1996, and much of what is offered under that name is worth very little. The specification permits 40-bit RC4, which was weak when it was standardized and is breakable in minutes now, and plenty of software still writes it by default.
This uses 256-bit AES, the strongest the format defines, and does not offer the alternatives. A protection you have to explain the limits of is not one worth choosing.
How it works
The file is passed to qpdf, which encrypts the document with the password you
supply and writes a new one. The password is set as both the user password and
the owner password, so it is needed to open the file at all rather than only to
print it.
Nothing is re-rendered. The pages, text, links and form fields are the ones from the original, wrapped in encryption rather than rebuilt.
The permissions trap
This is the part most people get caught by, and it is why the tool does not offer a choice here.
A PDF distinguishes two passwords. The user password is required to open the document. The owner password controls printing, copying text, and editing. If you set only the owner password — which several tools do by default, because it sounds like more control — the file opens for anyone who has it, and the restrictions are honored entirely at the reader's discretion. A great deal of PDF software simply ignores them.
That is protection in name only. Setting the same password as both is what somebody asking to protect a document actually wants, so that is what happens.
Write the password down first
There is no recovery. Not by us, because the password is never stored, and not by anyone else, because 256-bit AES does not have a weakness to exploit. If you lose it, the document is gone.
That sounds like a warning about this tool and it is really a description of encryption working. A protection that could be undone by asking nicely would not be protecting anything.
When to do it on your own machine instead
The file is unencrypted while it travels here and while it is processed, and is deleted within 30 minutes along with the result. For most documents that is a reasonable trade for not installing anything.
For something genuinely sensitive it is not, and the honest alternative is that qpdf is free software: one command on your own computer does exactly this, with the file never leaving it.
Examples
A contract going out by email
Email is not a private channel and forwards are easy. A password means the document is readable by the person you sent the password to, rather than by anyone the message reaches.
A document shared over a link
A link that gets passed on is out of your control. Encrypting the file means the link alone is not enough, which is a meaningful difference for anything with personal data in it.
Frequently asked questions
How strong is the encryption?
256-bit AES, which is the strongest the PDF specification defines and the only option offered here. PDF also permits 40-bit and 128-bit RC4, and the 40-bit variant is breakable in minutes by software anyone can download — a protection that mainly produces a false sense of one. There is no reason to offer the weaker settings, so they are not exposed.
What is the difference between a user and an owner password?
A PDF has two. The user password is needed to open the document at all; the owner password governs printing, copying and editing. Setting only the owner password produces a file that opens freely and merely asks readers politely not to print, which most PDF software ignores. This sets your password as both, which is what protecting a document normally means.
Can you recover the password if I lose it?
No. It is not stored anywhere — it reaches the encryption step and is gone when the request ends — and even if it were, 256-bit AES has no back door to walk through. A lost password means a lost document. Write it down before you download the file, not afterwards.
Is this as safe as encrypting the file myself?
The encryption is identical, because it is the same software doing it — qpdf, which is free and runs on your own machine. What differs is that the unencrypted file passes through our server for the length of the operation, and is deleted within 30 minutes along with the result. For a genuinely sensitive document, doing it locally removes that step entirely, and that is a fair thing to prefer.
Further reading
- Rotating Every Page of a PDF Cost 29 BytesA rotated PDF looks like a document that has been redrawn, so people expect rotating one to cost something — quality, size, or both. It costs almost nothing, and understanding why tells you which other PDF operations are safe and which are not.
- What a PDF Password Actually Costs, in Bytes and in ProtectionPutting a password on a PDF costs almost nothing in size, which is the least interesting thing about it. The interesting part is that a PDF can carry two completely different kinds of password, and only one of them is protection.