Put a password on a PDF
Encrypt a PDF with a password free, with no signup. The password never leaves your machine, and the page is honest about which restrictions actually hold.
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How it works
The document is re-serialised with an encryption dictionary. Your password is run through the algorithm named there to derive a key, and every string and stream in the file is encrypted with it before writing. The permission bits are stored alongside as a small integer. The cipher chosen depends on the PDF version the file declares, which is why an old document may be encrypted to an older standard than a modern one.
What to watch out for
Printing, copying and editing restrictions are numbers written into the document. Well-behaved readers obey them; a great many do not, and anyone who can open the file can extract its text with a few lines of code. Only the password itself actually stops someone.
The key is derived from your password, so the password is the weakest part of the whole scheme. Four random words beat one word with digits and punctuation substituted into it, because the attack that matters tries patterns rather than characters one by one.
PDFs can carry a flag telling assistive technology to keep out. This tool always leaves it on and does not offer the choice, because disabling it protects nothing from anyone who can already open the file and makes the document unusable for blind readers.
Limits
Files up to about 100 MB work reliably. Beyond that, the ceiling is your device's memory rather than any rule we impose — the work happens on your own machine. Tested in Chrome 140, Firefox 143, Safari 18.
What actually protects the file
One thing: the password. It derives the key that the document’s contents are encrypted with, and without it there is nothing to read — not with a different reader, not with a hex editor, not with patience.
Everything else on this page is weaker than that, and the difference is worth understanding before you rely on it.
Why the permission tick boxes are not security
A PDF stores its restrictions as a small integer: bit three means printing is allowed, bit five means copying, and so on. That integer travels inside the document and asks readers to behave.
Adobe Reader obeys it. Preview on a Mac largely obeys it. A great many other readers, and every programming library, do not — and a person who can open your document can extract its text in about three lines of code regardless of which boxes you tick here.
They are worth setting anyway, because they stop the accidental case: a colleague who would not have copied your text on purpose but whose reader now greys the option out. They are not worth trusting for anything that would hurt if it leaked.
Choosing a password that is worth the encryption
The cipher is not the weak point. The password is, because the key is derived from it, and an attacker with the file can try candidates as fast as their hardware allows without anyone noticing.
Four unrelated words are far stronger than one word with a digit on the end and an exclamation mark after it — that substitution pattern is the first thing any cracking tool tries. Length is what buys time; punctuation mostly buys inconvenience for you.
Write it down somewhere safe. There is no recovery for a PDF password, here or anywhere, and the companion tool on this site deliberately refuses to guess one.
Nothing is uploaded, including the password
The encryption runs in a Web Worker in your browser. The document is never transmitted, and the password you type is never sent, stored or logged — it exists only in the memory of the tab you are looking at.
That is worth more here than on most tools. A service that encrypts your PDF on its own servers has, however briefly, held both your document and the password to it.
Your files never leave your browser. Last updated 2026-08-02.
Next step
Your file is already here in this browser, so the next tool starts with it loaded.
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