Protect PDF with Password
Add an open password to any PDF and encrypt it with AES-256, the strongest standard PDF encryption. You can also restrict printing, copying and editing. The file is encrypted on your own device and never uploaded.
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1. Set an open password
Use 12+ characters, or a few random words.
2. Permissions optional
Lets you change the permissions later. Leave it blank and a random one is used.
Without restrictions, anyone with the open password can print, copy and edit.
Store the password somewhere safe. A lost open password cannot be recovered from an AES-256 PDF.
How to use the Protect PDF with Password
- Choose your PDF by dropping it into the box or clicking to browse.
- Type an open password twice, or press Generate strong password and save it somewhere safe.
- Optionally restrict permissions: tick the box, set a permissions password and choose what is allowed.
- Press Protect PDF. Encryption takes a second or two.
- Download the protected PDF and check it by opening it: your PDF reader will ask for the password.
Open password vs. permissions password
A PDF can carry two different passwords, and this tool lets you set either or both:
| Password | Also called | What it does | Strength |
|---|---|---|---|
| Open password | User password, document open password | Needed to view the file. Without it the content cannot be decrypted. | Strong: protected by AES-256 encryption |
| Permissions password | Owner password, master password | Controls printing, copying, editing, commenting and page assembly. | Enforced by PDF apps that follow the standard |
If you only want to stop casual copying of a document you publish openly, set permissions without an open password. If the content is confidential, always set an open password.
What the encryption covers
This tool uses the PDF standard security handler with AES-256 (encryption dictionary V 5, R 6, crypt filter AESV3), defined in ISO 32000-2 (PDF 2.0). Every content stream, image, font, form field value, annotation and bookmark title is encrypted with a random 256-bit file key, and each string and stream gets its own random initialization vector. The file key itself is wrapped with keys derived from your passwords using the standard's iterated SHA-256/384/512 hash, which makes password guessing slower.
- The page structure (number of pages, page sizes) stays visible, as in every encrypted PDF.
- The title, author and other metadata are encrypted too, unless you untick that option to keep them searchable.
- Digital signatures are invalidated by encryption, so protect the PDF before signing it.
Choosing a good PDF password
Encryption is only as strong as its password. Attackers who get the file can try passwords offline at high speed, so length matters more than complexity:
- Use at least 12 to 16 random characters, or a passphrase of four or more random words.
- Avoid names, dates, keyboard patterns and passwords you use elsewhere.
- Send the password through a different channel than the file, for example the PDF by email and the password by text message or phone.
Frequently asked questions
How do I password protect a PDF for free?
Open the PDF in this tool, type a password in both boxes and press Protect PDF, then download the file. Anyone who opens the new PDF must enter the password. The encryption runs in your browser, so the document is not uploaded anywhere.
How secure is AES-256 PDF encryption?
AES-256 is the strongest encryption defined by the PDF standard (ISO 32000-2) and is not known to be breakable. The weak point is the password: a short or common password can be guessed by trying millions of combinations, so use at least 12 random characters or several random words.
What is the difference between the open password and the permissions password?
The open password (user password) is needed to view the file at all. The permissions password (owner password) controls restrictions such as printing and copying. Someone who opens the file with the open password gets only the permissions you allowed, while the permissions password unlocks everything.
Can someone remove the printing and copying restrictions?
Restrictions are enforced by PDF apps that follow the standard, such as Adobe Acrobat, Chrome and Preview, but they are not as strong as the open password. Anyone who can open the file could use other software to ignore them. To keep a document confidential, always set an open password.
Will the protected PDF open on phones and in Preview?
Yes. AES-256 PDFs open in Adobe Acrobat and Reader (version X and later), Chrome, Edge, Firefox, macOS and iOS Preview, and Android PDF viewers. Very old readers from before 2010 may not support AES-256.
What if I forget the password?
There is no back door. A strong AES-256 password cannot be recovered, so keep a copy of the original unprotected PDF or store the password in a password manager.
Does protecting a PDF change its content or size?
No. Pages, text, images, links and form fields stay exactly the same. The file size usually changes by only a few kilobytes because every part of the file is encrypted rather than recompressed.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.