Protect PDF with Password

How do I password protect a PDF?

1. Drop one or more PDFs onto the drop zone, or click it to choose them.
2. Type a strong Password to open; this is what readers will need.
3. Optionally type an Owner password (optional) to control permissions separately, or leave it blank to use the same password.
4. Tick or untick Allow printing and Allow copying text.
5. Click Protect PDF.
6. Download the protected PDF, or click Download all as ZIP for several files, and share the password separately.

Protect PDF encrypts the whole file with AES-256, the strongest encryption the PDF standard supports and the same cipher used for online banking, using pdf-lib in your browser. Every page, image and piece of text inside the file is scrambled so that without the password a viewer cannot show anything at all. Text stays selectable and searchable for anyone who does have the password, and the file size barely changes.

The two passwords do different jobs. The Password to open is the one readers type to see the document; it is the protection that matters. The Owner password (optional) is a second key that lets its holder change the permissions or remove the encryption later, and it governs the permission tick boxes. If you leave it blank the open password is used for both, which is fine for most personal use. Set a different owner password when you want people to read a document but not to lift the restrictions.

Allow printing and Allow copying text set the permission flags. These are honoured by Adobe Reader, Preview, Chrome and most mainstream viewers, so a reader without the owner password will find the print or copy commands greyed out. They are not a cast-iron guarantee: anyone with the open password can still take a screenshot or photograph the screen, and some third-party software ignores the flags. Treat the permissions as a clear statement of intent and rely on the open password for real confidentiality.

Choose a password of at least 12 characters mixing letters, numbers and symbols, and send it by a different channel from the file, such as a text message when the PDF goes by email. There is no way to recover a forgotten password from the file, and Kilnfile cannot help because nothing is stored. Several PDFs can be protected with the same settings at once and come back as a ZIP. There is no file size limit beyond device memory, no signup and no watermark, and the PDF and your passwords never leave your device.

How it works: this tool uses pdf-lib and PDF.js (Mozilla), open-source libraries loaded into your browser. No server is involved, so Kilnfile never sees your file. Last reviewed 20 September 2026.

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