Drop in a PDF, set a password, and download a locked copy that asks for that password before it will open. It's real 256-bit AES encryption, the same standard used for sensitive documents — not a flimsy "open password" a viewer can ignore. Need to go the other way? Drop in a PDF you can already open, enter its password, and get an unlocked copy back.
Every step runs in your browser tab. The PDF and the password never leave your device — nothing is uploaded, stored, or used for training. The encryption engine (qpdf compiled to WebAssembly) downloads once and is cached, so after that you can flip on airplane mode and it still locks and unlocks.
Add the PDF you want to lock — a contract, statement, medical record, or report. It loads straight into the browser tab with no upload step and no account. A locked PDF you already have a password for works here too, for unlocking.
Type the password the file should require. qpdf-wasm encrypts the document on your device with 256-bit AES, applying the password as both the user and owner password, so the lock holds whoever opens it. You download a sealed -protected.pdf.
Anyone with the password and a normal PDF viewer can open the protected file — no nimbril needed. To strip the lock again, drop the file back in, enter the password, and download an unlocked copy. A wrong password fails cleanly without revealing anything.
A settlement agreement or discovery packet often has to go out by email, where a forwarded message or shared inbox can expose it to the wrong eyes. Locking the PDF with AES-256 means the file is useless to anyone without the password, and because the encryption happens on your laptop, the privileged document never passes through a third-party server. Share the password through a separate channel — a call or text — and the protection holds end to end.
Patient summaries, EOBs, offer letters, and disciplinary records are exactly the files you don't want sitting unencrypted in an email thread. Add a password before sending so the document is protected at rest and in transit, and keep the whole step on-device to sidestep the business-associate-agreement question an upload tool would raise. For HIPAA-covered or NDA-bound material, "never uploaded" is the part you can put in writing.
Bank statements, payroll summaries, and vendor invoices carry account numbers and totals that shouldn't travel in the clear. Encrypt the PDF so an auditor or counterparty needs the password to open it, then batch-lock a month of statements with one password on Pro and download them as a ZIP. The files are sealed on your machine before they ever leave your outbox.
Tax returns, passport scans, and lease agreements are the documents most worth locking before you store them in cloud storage or email them to a landlord, accountant, or family member. Drop the PDF in, set a password you'll remember, and download a copy that asks for it. No install, no account to try, and the original file never leaves your browser.
When you protect a PDF, nimbril runs qpdf — a long-trusted PDF library — compiled to WebAssembly inside your tab, and rewrites the document with 256-bit AES encryption. Your password becomes both the user password (what's needed to open the file) and the owner password (what controls permissions), so there's no weaker secondary password that quietly unlocks it. The honest trade-off is that this is a single-password lock, not a per-recipient permissions system: anyone you give the password to can open the file and, using this tool, can also remove the password. It also can't crack a PDF you don't have the password for — there's no brute-forcing here, by design. The encryption strength comes from your password, so a short or obvious one is the weak link; pick something long and unique.
It's a strange contradiction that many "password protect PDF" sites ask you to first upload the very document you're trying to keep private — so before it's encrypted, the unprotected file (and sometimes the password) sits on a stranger's server. nimbril inverts that: the PDF is read into your browser and encrypted there, so the plaintext document is never transmitted, never stored, and never used for training. The verifiable proof is airplane mode — once the ~1.3 MB engine has cached, cut your network and it still locks and unlocks, because there was never a round-trip to begin with. For anything under HIPAA, an NDA, or attorney-client privilege, that means there's no upload to account for and no "where did our document go" question to answer later.
No. The encryption runs entirely in your browser using qpdf compiled to WebAssembly, so the PDF and the password never leave your device — nothing is uploaded, stored, or transmitted. After the engine downloads once and caches, you can switch on airplane mode and it still works, which is the proof it's truly on-device.
It's genuine 256-bit AES encryption, not a soft "please don't open" flag that some readers ignore. The document's contents are actually encrypted, so a standard PDF viewer will require the correct password before it shows a single page. The same password is set as both the user and owner password, so there's no second password that quietly bypasses the lock.
Yes, as long as you know the password. Drop the locked PDF in, switch to unlock, and enter the password to download a copy with the encryption removed. It cannot crack or guess a password you don't have — if the password is wrong it simply fails with "wrong password" and nothing is revealed.
There's no recovery and no backdoor. Because nothing is uploaded and the password is never stored anywhere by nimbril, a forgotten password means the file stays locked — that's the point of real encryption. Keep the password somewhere safe, ideally a password manager, before you send the protected file off.
Yes — protecting and unlocking a single PDF is free, with no signup to try. Pro is $9/mo or $69/yr and unlocks batch protecting (lock a whole folder with one password), ZIP download, larger files, no watermark, and unlimited history across every nimbril tool. There's also a $4/mo single-app plan for just this tool.
Yes. AES-256 PDF encryption is a standard format, so the locked file opens in Adobe Acrobat, macOS Preview, Chrome, Edge, and the PDF viewers on iOS and Android — each will prompt for the password. The recipient doesn't need nimbril or any special app, just the password.
Yes, on Pro. Batch mode lets you drop in many PDFs, protect them all with one password, and download them together as a single ZIP — handy for a stack of statements or a set of exhibits. Everything still happens on your device; batching never sends anything to a server.