# Password-Protect a PDF — Real AES Encryption, In Your Browser > Encrypt a PDF with a password using AES-128, and choose what readers are allowed to do. To password-protect a PDF, add the file and set an open password. The document is encrypted with the PDF standard security handler using AES-128 — real encryption, performed in your browser, so the file and the password never leave your device. Anyone opening the result is asked for the password by every PDF reader. You can also restrict printing, copying and editing, though those restrictions are a request that readers honour rather than something enforced by the cipher. **URL:** https://convertto.tech/t/protect-pdf **Category:** PDF Tools (https://convertto.tech/c/pdf-tools) **Privacy:** Runs entirely in the browser; no upload **Cost:** Free, no sign-up **Last updated:** 2026-08-01 ## Key facts - **Cipher:** AES-128 in CBC mode, or RC4-128 for legacy readers - **Handler:** PDF standard security handler, revision 4 - **Privacy:** Runs entirely in your browser — nothing is uploaded - **Cost:** Free, unlimited, no sign-up ## How to use 1. Select your pdf file — the file stays on your device and is never uploaded. 2. Enter or paste your open password. 3. Enter or paste your owner password. 4. Choose the cipher. 5. Turn "Allow printing" on or off as needed. 6. Turn "Allow copying text" on or off as needed. 7. Turn "Allow editing" on or off as needed. 8. Turn "Allow comments" on or off as needed. 9. Turn "Allow filling forms" on or off as needed. 10. Turn "Allow reordering pages" on or off as needed. 11. Turn "Allow screen readers" on or off as needed. 12. Press Run, then download the result when it is ready. ## FAQ ### Is this real encryption or just a restriction flag? Real encryption. Every string and every content stream in the document is encrypted with a key derived from your password, exactly as the PDF specification defines. You can confirm it: open the protected file in a text editor and the words that were in the document are no longer there. Tools that only set a "do not print" flag leave the text sitting in plain sight. ### AES-128 or RC4-128? AES-128 unless you have a specific reason. It is what every reader made since about 2005 supports. RC4 is cryptographically broken and is offered only for genuinely ancient software — treat it as a compatibility setting, not a security one. ### What is the owner password for? It separates two rights. The open password lets someone read the document; the owner password lets someone change the permissions. Set only an open password and the two are the same, which means anyone who can read the file can also lift its restrictions. ### Can I recover the file if I forget the password? No, and nobody else can either. That is the point of encryption. Store the password somewhere before you close this tab. ### Do the permission settings actually stop anyone? They stop well-behaved readers, which in practice is most people most of the time. They do not stop software that chooses to ignore them, because anything that can decrypt the file to display it can also print it. Use permissions to express intent, and the password for security. ## Sources - [ISO 32000-1 §7.6 — Encryption](https://www.iso.org/standard/51502.html) — ISO ## Related tools - [Unlock PDF Password](https://convertto.tech/t/unlock-pdf): Decrypt a PDF you have the password for, or strip owner restrictions that need no password at all. - [Redact PDF](https://convertto.tech/t/redact-pdf): Black out names, figures or images so they are genuinely gone, not just hidden behind a box. - [Crop PDF](https://convertto.tech/t/crop-pdf): Trim the margins of every page, or just the pages you choose, without re-rendering. - [Duplicate PDF Pages](https://convertto.tech/t/duplicate-pdf-pages): Repeat chosen pages any number of times — for labels, tickets, forms or handouts. - [Edit PDF](https://convertto.tech/t/edit-pdf): Add text, pictures, shapes, arrows, highlights and freehand drawing to any PDF page. - [Excel to PDF](https://convertto.tech/t/excel-to-pdf): Convert an Excel workbook to a PDF table, one section per sheet, in your browser. - [Extract PDF Pages](https://convertto.tech/t/extract-pdf-pages): Pull specific pages out of a PDF into a new document, in one file or one file per page. - [Fill PDF Forms](https://convertto.tech/t/fill-pdf): Read a PDF's interactive form fields, fill them in, and optionally lock the answers.