🔒 PDF Tools

Password-Protect a PDF

Add a password to a PDF so only people with the password can open it. The file is encrypted with strong AES-256 right in your browser — set your password and download the protected PDF, with nothing uploaded.

✓ Free forever✓ No upload✓ No signup✓ In your browser

📂

Drop a PDF to protect

or click to browse · one PDF file

✅

PDF protected!

⬇ Download PDF

In short: drop a PDF, type a password, and download the encrypted file. It uses AES-256, the strongest encryption the PDF format defines, and it runs entirely on your device — so neither the document nor the password is ever sent anywhere. There is no account and no limit on how many you do.

How strong is the encryption?: AES-256, which is what the PDF specification calls its strongest. The document is genuinely encrypted, not merely flagged as restricted — without the password there is nothing to read.
Is my file or password uploaded?: No. The encryption runs in your browser, so neither leaves your device. For a password tool that is the whole question: uploading a confidential PDF to get it protected is backwards.
Can I allow opening but block printing?: No. This sets one password that is required to open the file. Print and copy restrictions are a separate mechanism, and one every PDF reader is free to ignore.
What if I forget the password?: The file is unrecoverable. That is what real encryption means — there is no master key and no reset, here or anywhere. Keep it in a password manager before you close the tab.
Is there a task or size limit?: No. Sejda allows 3 tasks an hour on its free tier and Smallpdf 2 a day; there is no server here to protect, so there is nothing to meter.
Can I protect a PDF that is already encrypted?: Not directly — unlock it first with the password you have, then protect it with the new one. The tool says so rather than failing obscurely.

How to Password-Protect a PDF

Add Your PDF

Drop the PDF onto the tool, or click to browse and select it.

Set a Password

Type the password that will be required to open the file.

Click Protect

qpdf encrypts the PDF with AES-256 in your browser — nothing uploaded.

Download

Download the protected PDF; anyone opening it must enter the password.

Why Use Convertlo?

🔒 100% Private — the PDF and password never leave your browser
🆓 Free forever — no account, no watermark, no limits
🛡️ AES-256 encryption — strong, modern PDF encryption
🔑 Open password — the file prompts for the password before opening
🧩 Real qpdf engine — industry-standard encryption via WebAssembly
📱 Works on mobile — any modern browser, any device

Features

🔒

100% Private

No server, no upload — the file and password stay on your device.

🛡️

AES-256

Strong, modern encryption applied to the whole file.

🔑

Open Password

Readers must enter the password to open it.

🧩

qpdf Engine

The industry-standard PDF tool, in WebAssembly.

⚡

Instant

Encrypts in seconds.

📱

Mobile-Ready

Works on iPhone, Android, tablet, and desktop.

Encryption and permissions are not the same thing

"Protect" covers two completely different things in the PDF world, and most tools do not tell you which one they are doing.

Real encryption

The document’s contents are encrypted with a key derived from your password. Without the password there is nothing to read — not slow to read, not awkward to read: nothing. This is what this page does, at AES-256, which is the strongest scheme the PDF specification defines.

Permissions

The other kind sets flags saying "do not allow printing" or "do not allow copying" and leaves the content unencrypted. Every reader is free to honour or ignore those flags, and plenty ignore them; removing them takes seconds and no password at all. It is a request, not a restriction. This page does not offer it, because offering it implies a protection it does not provide.

The engine is qpdf, the same library the command-line world has used for this for twenty years, compiled to WebAssembly and served from this site rather than a CDN. That matters for a security tool: the code doing the encryption is a file you can inspect at /vendor/qpdf/, not a third-party script that could change under you.

Why one password rather than two

A PDF can carry two passwords. The user password is the one that opens the file. The owner password is the one that changes its permissions. Together they allow a setup where anyone can read the document but only the owner can, say, enable printing.

This tool sets the same password as both, deliberately. The alternative is the arrangement described above, where the file opens for anyone and the restrictions rest entirely on readers choosing to obey them — which, as the previous section says, they often do not. A tool offering that as "protection" would be selling a lock with no bolt.

So the model here is simple and honest: one password, required to open, real encryption behind it. If what you actually need is "anyone can read it, nobody can print it", no PDF tool can genuinely give you that — the content has to be readable to be displayed, and once it is on screen it can be captured.

There is no recovery, and that is the point

Everything here runs on your device, which means we cannot help you if the password is lost. There is no master key, no recovery link and no record of what you typed — not as a policy, but structurally, because nothing was ever sent. That is the point of the tool, and it is also its sharpest edge.

So, practically:

Put the password in a password manager before you close the tab. Not in the filename, and not in the email you send the PDF with — an attachment and its password in the same message is the commonest way this protection is wasted.
Send the password by a different channel. A message, a call, anything that is not the thread carrying the file.
Keep an unencrypted original somewhere safe if the document matters. Encryption protects against the wrong reader, not against your own forgetfulness.

A word on strength: AES-256 is not the weak link. A short or guessable password is, because the key is derived from it. Four random words beats a clever substitution of a word somebody could guess.

Capabilities at a glance

What this tool does and does not do, stated plainly. The “No” rows are the point, not an omission.

Capability	Supported	Detail
Encryption
AES-256	Yes	The strongest encryption the PDF specification defines. Real qpdf, compiled to WebAssembly.
A password required to open the file	Yes	Without it there is nothing to read.
Separate owner and user passwords	No	One password is set as both — see below.
Print, copy or edit restrictions	No	A different mechanism, and one readers are free to ignore.
Choosing AES-128 or RC4 instead	No	AES-256 always. The older schemes exist for compatibility with very old readers.
Certificate or identity-based encryption	No	Password only.
Input
Any PDF	Yes	Including scans and forms.
An already-encrypted PDF	No	Unlock it first with Unlock PDF, then protect it again.
File size limit	No	There is no server to protect. Sejda caps the free tier at 50 MB and 50 pages; iLovePDF at 25 MB.
Task limit	No	Smallpdf allows 2 free tasks a day, Sejda 3 an hour. There is nothing to meter here.
Several PDFs at once	No	One at a time.
Output
A standard encrypted PDF	Yes	Opens in Acrobat, Preview, Chrome and every reader that supports AES-256.
The original left untouched	Yes	The result is a new download; your file is not modified.
Watermark	No	Nothing is added to the pages.
Password recovery	No	There is none. Forget it and the file is gone.
How it runs
Nothing is uploaded	Yes	Neither the document nor the password leaves your device.
Signup	No	There is no account.
Offline use	No	The page and the ~1.3 MB engine load from the network first.

Frequently asked questions

It uses AES-256, the strongest encryption the PDF specification defines. The document’s contents are genuinely encrypted with a key derived from your password — without it there is nothing to read. This is not a "restricted" flag that a reader can ignore; the bytes themselves are unreadable.

No, neither. The encryption runs inside your browser using qpdf compiled to WebAssembly, so the document and the password both stay on your device. For a password tool this is the whole question: uploading a confidential file to a stranger’s server in order to protect it is backwards, and every large free PDF site does exactly that.

Encryption scrambles the content so it cannot be read without the password. Restrictions are flags saying "do not print" or "do not copy" attached to a file that is otherwise perfectly readable, and every PDF reader is free to ignore them — plenty do, and stripping them takes seconds. This tool does the first. It does not offer the second, because calling that protection would be misleading.

Not here, and not meaningfully anywhere. That arrangement leaves the content unencrypted and relies on the reader software choosing to obey a flag. If the document is readable on screen it can be screenshotted, and if it is unencrypted the restriction can be removed without any password at all.

The file is unrecoverable. There is no master key, no reset and no record of what you typed — not as a policy but structurally, because nothing was ever sent anywhere. Save the password in a password manager before you close the tab, and keep an unencrypted original if the document matters.

No, to both. There is no server here to protect, so there is nothing to meter. For comparison, checked in September 2026: Sejda’s free tier allows 3 tasks an hour with a 50 MB and 50-page cap, Smallpdf allows 2 tasks a day, and iLovePDF roughly 1–2 an hour with a 25 MB cap on most tools.

Not in one step. Unlock it first with Unlock PDF using the password you have, then protect the result with the new one. The tool tells you this rather than failing with an unexplained error, which is what happens if you try.

Any reader that supports AES-256, which is all current ones: Acrobat, Preview on macOS and iOS, Chrome, Edge, Firefox and the standard Android viewers. Very old software — Acrobat 8 and earlier — predates AES-256 and will not open it. That is the trade for using the strongest option rather than an older one.

Because they are weaker and the only reason to pick them is compatibility with readers from before about 2008. Offering a choice would mostly result in people choosing the weaker one by accident. If you genuinely need to support a very old reader, the desktop qpdf command line will do it.

It cannot. The password is read from the field, passed to the encryption engine running in the same tab, and that is the end of it — there is no request that could carry it and no storage it is written to. You can confirm the first part in your browser’s Network tab: the only requests this page makes are for itself and the engine.

The encryption itself is near-instant for an ordinary document. The engine is about 1.3 MB of WebAssembly, fetched the first time you use the tool and then cached by the browser, so the first run has a short pause and later ones do not.

It is qpdf — the library the command-line world has used for this for two decades — compiled to WebAssembly and served from this site rather than a CDN. That is deliberate for a security tool: the code doing the encryption is a file at /vendor/qpdf/ that does not change unless we change it, rather than a third-party URL that could serve something else tomorrow.

No. The pages, text, images and form fields are exactly as they were; what changes is that they are stored encrypted. Your original file is not modified either — the result is a new download.

Only until they open it. Once the correct password has been entered the document is a normal PDF on their machine, and they can select, copy, print or re-save it. Encryption controls who gets in, not what they do afterwards. Anyone telling you otherwise is selling the permissions flags described above.

Yes — more than the cipher does. AES-256 is not the weak link; a short or guessable password is, because the key is derived from it. Four random words is far stronger than a clever-looking substitution of a word that could be guessed, and easier to pass on.