A contract sent by email
- Input
- contract.pdf, password set, copying blocked
- Output
- An encrypted PDF that prompts for a password on open
Send the password separately — by phone or message — rather than in the same email as the file.
Protect PDF
Protecting a PDF encrypts its contents so it cannot be opened without the password. This tool applies AES-256 encryption, the strongest option in the PDF specification, and can also restrict printing, copying and editing. Encryption happens in your browser, so neither the file nor the password is ever sent anywhere.
Encryption runs in your browser. Neither your file nor your password is uploaded.
How to
How to use Protect PDF
- 1
Upload the PDF
Drop a PDF onto the upload area or click to browse.
- 2
Set a password
Type the password needed to open the document, then confirm it. A strength indicator shows how solid it is.
- 3
Choose permissions
Optionally allow or block printing, copying, editing and annotating, and set a separate owner password to control them.
- 4
Encrypt and download
Click Protect PDF and save the encrypted file. Test it opens with your password before sending it on.
Examples
Protect PDF examples
A read-only handout
- Input
- handout.pdf, owner password set, printing allowed, editing blocked
- Output
- A PDF that opens freely but refuses edits in compliant readers
With only an owner password set, anyone can open the file, but permissions restrict what they can do with it.
Payroll records for storage
- Input
- payroll.pdf, strong password, printing and copying blocked
- Output
- An AES-256 encrypted PDF
Encryption strength depends on the password. A long, unusual passphrase is what makes AES-256 worth having.
Why use it
What Protect PDF gives you
AES-256 encryption
The strongest algorithm the PDF format supports, and the same standard used for encrypted disks and archives.
Password never transmitted
Encryption happens on your device, so your password is never sent to or stored on any server.
Permissions as well as passwords
Block printing, copying, editing or annotating independently of whether a password is needed to open the file.
Strength feedback while typing
The strength meter shows immediately whether your password is long and varied enough to be worth using.
Works in every standard reader
Standard PDF encryption is understood by Acrobat, Preview, Chrome, Edge and mobile readers alike.
Good to know
Protect PDF limitations
- There is no password recovery. If you forget the password, the file cannot be opened — keep a copy somewhere safe.
- Permission settings are honoured by well-behaved readers but are not a hard technical barrier; the open password is the real protection.
- Encrypting an already-encrypted PDF is not supported. Unlock it first.
- Files are limited to 50 MB.
Summary
Protect PDF in short
- AES-256 encryption is applied in your browser; the password is never transmitted.
- An open password controls who can read the file; permissions control what they can do with it.
- A forgotten password cannot be recovered by anyone, including us.
- Encryption is only as strong as the password you choose.
FAQ
Protect PDF questions
How strong is AES-256 encryption on a PDF?
The algorithm itself is not practically breakable by brute force. In real terms the weak point is the password — a short or common one can be guessed regardless of the algorithm behind it.
What if I forget the password?
The file cannot be opened. There is no backdoor and no recovery process, including for us, because the password is never sent to or stored on any server.
What is the difference between the user and owner password?
The user password is required to open the document. The owner password governs permissions such as printing and editing. Setting only an owner password lets anyone open the file while still restricting what they can do.
Do the permission settings actually stop people?
They are instructions that compliant readers follow. Acrobat and mainstream browsers respect them, but some tools ignore them. Use an open password when the content genuinely must stay private.
What makes a good PDF password?
Length matters most. Four unrelated words are stronger and easier to remember than a short string of symbols. Avoid names, dates and anything reused from another account.
How should I send the password to someone?
Through a different channel from the file. Emailing the PDF and its password together means one compromised inbox exposes both.
Can I add a password to an already-protected PDF?
No. The existing encryption has to be removed first with the Unlock PDF tool, after which you can apply a new password and permissions.
Will the protected file open everywhere?
Yes. This uses standard PDF encryption, so Acrobat, macOS Preview, Chrome, Edge and mobile readers all prompt for the password normally.
Does encrypting change the document itself?
No. Pages, text, images and formatting are unchanged. Only a security layer is added, so the file size grows very slightly.
Discover
Related PDF tools
Unlock PDFRemove the password from a PDF you own. Text stays selectable and quality is unchanged. Enter the password to decrypt.Merge PDFCombine multiple PDFs into one file. Drag to set the page order, then download. Runs in your browser — no upload, no sign-up.Compress PDFShrink a PDF so it fits an email or upload limit. Choose a quality level and see the exact size saved before you download.Split PDFSplit a PDF into single pages or custom ranges and download them individually or as a ZIP. Runs in your browser, no sign-up.Edit PDFEdit the text already in your PDF, add new text, sign, highlight and place images. Runs in your browser — no upload, no sign-up.Extract PDF PagesPick the pages you want and save them as a new PDF. Click thumbnails or type ranges. Runs in your browser, no sign-up.Delete PDF PagesRemove blank or unwanted pages from a PDF. Click thumbnails to mark pages for deletion, then save the trimmed file.JPG to PDFTurn JPG, PNG or WebP images into one PDF. Set page size, orientation and margins, reorder pages, then download.