How to keep a PDF safe before you share it
A PDF usually leaves your hands by email or upload, and once it's gone you can't pull it back. Securing it beforehand means deciding who may open it, showing who approved it and making sure the version you send is the one you meant to send.
Every tool here is free. None of them needs an account or adds a watermark.
Choose a Security ToolWhich tool covers which risk
Each tool answers one question about the file, and each leaves a gap that another tool or a habit has to close. Check the last column before you lean on any one of them alone.
| The risk | Tool | What it does not cover |
|---|---|---|
| The wrong person opens the file | Protect PDF | Sets no print or copy limits: whoever has the password can do everything |
| Someone reads text that should be hidden | Redact PDF | Only removes what you mark or search for, so check every page |
| The file was changed before it came back | Compare PDFs | Compares wording only, not images or formatting, and a scan needs OCR first |
| Nobody can show who approved it | Sign PDF | Places a picture of your signature, with no certificate behind it |
| You need to open a file you locked | Unlock PDF | Needs the password and can't guess one |
Protect PDF encrypts with 256-bit AES through qpdf and sets the same password as both passwords of the file. The guide to owner and user passwords explains why that leaves no separate permissions, and the AES-256 compatibility guide covers which readers open the result.
The order to prepare a PDF for sharing
Flatten first, then redact, then check the document properties, and add the password last. Flatten, Redact and the editing tools all refuse a PDF that needs a password to open, with the message "This PDF is password protected. Remove the password with Unlock PDF first."
Why flatten before redacting? A filled form field isn't page text yet: on our form, a search for a word shown in a form field found 0 matches before flattening and 1 after. Flatten PDF sits with our PDF optimize tools, and you change the title and author fields with Edit PDF Metadata from our PDF editing tools.
Sign before you protect, so the signed copy is the one that gets the password. If the other side sends the document back, compare it with your copy before you sign it.
One file through the whole chain
We ran a one-page form (6.9 KB, with fields) through the four steps on 22 October 2026. It got smaller at each step until the password went on.
| Step | Size after it | What changed |
|---|---|---|
| Flatten PDF | 3.0 KB | The form fields were gone; their text stayed on the page |
| Redact PDF, one word from the form, metadata ticked | 1.1 KB | One match removed; before flattening the same word gave 0 matches |
| Edit PDF Metadata, new title only | 1.2 KB | Title set to a neutral name |
| Protect PDF | 1.9 KB | AES-256 encryption, all permissions allowed |
Run it in the other order and the chain stops right away: Flatten refused the protected copy with the message quoted above. Redact already clears the metadata when its box is ticked, so you only need Edit PDF Metadata to set a new title or author.
When you receive a PDF instead
A file that opens without a password but blocks printing or copying carries only an owner password. Our editing tools take a file like that and hand back a copy without the limits, while Unlock PDF needs the owner password for it.
Got a contract back? Run Compare PDFs against the version you sent. It reports every changed line from both files, which a quick read through the pages tends to miss.
Frequently Asked Questions about PDF Security
How secure is a password-protected PDF?
The content is encrypted with 256-bit AES, so nobody reads the file without the password. A short or common password is the weak spot, so use a long one and send it some other way than the PDF.
With a password, can someone read the title or page count without opening it?
No. We protected a file whose title, author and attachment held readable text, then tried to open it without the password. Every tool we tried refused it, and the title, author and even the page count were unreadable, because a user password encrypts the metadata too.
Can you recover a password I forgot?
No. Unlock PDF needs the password, and nothing on this site guesses or cracks one.
Can I redact or flatten a PDF after I protected it?
Not directly. Remove the password with Unlock PDF, make the change, then protect the new copy again.
Are my files stored?
Signing happens in your browser; eSign a PDF without printing and scanning walks you through it. Files uploaded to the other tools get deleted from our server within two hours.