Password Protect a PDF
Encrypt a PDF so only people with the password can open it.
- Browser-based — no install
- Files private to your account
- Up to 250 MB on Pro
Encrypt a PDF so only people with the password can open it. Unlike “print disabled” viewer flags that any tool can ignore, real password protection scrambles the file bytes — without the password, the content is unreadable. Useful for contracts, tax returns, medical records, and anything you wouldn’t email without a lock on it.
How it works
Right in your browser, no install
Flint PDF runs entirely in your browser. Drop a file in, do the thing, get the file out.
- 1
Upload your PDF
Drop in any PDF that doesn’t already have a password. (For locked files, use our Unlock PDF tool first.)
- 2
Pick a strong password
A long passphrase is better than a short complex one. We don’t store your password anywhere — if you forget it, the file is gone for good.
- 3
Download the encrypted PDF
The new PDF requires the password to open in any reader — Acrobat, Preview, Chrome, mobile apps, all of them.
What it's for
Built for real work
Send a contract by email
Lock the PDF before attaching it. Even if the wrong inbox receives it, the contents stay private.
Share tax returns or medical records
Sensitive financial or health PDFs benefit from a layer of encryption on top of HTTPS.
Lock a draft until launch
Distribute a preview to a small group with a shared password, then re-issue an unlocked version later.
FAQ
Frequently asked questions
- When does Password Protect launch?
- It's in active development — we'll announce when it's live. In the meantime, Adobe Acrobat, Preview (macOS), and many third-party tools can password-protect PDFs locally.
- Will it be real encryption?
- Yes. Flint uses standard PDF encryption (AES-256) — the same algorithm Acrobat uses. It’s not a viewer hint that can be bypassed; without the password the file is genuinely unreadable.
- What happens if I forget the password?
- We don’t store passwords anywhere. If you forget it, the file can’t be recovered. Use a password manager.
- Can the password be removed later?
- Yes, with our Unlock PDF tool — you provide the current password and we produce an unprotected version.
- Are my files private?
- Yes. Files are processed only for the action you trigger and never shared. The password never leaves your account.
- What's the maximum file size?
- Flint Pro accepts PDFs up to 250 MB.
- Can I set different read vs edit passwords?
- We plan to support both “document open” and “permissions” passwords (the second blocks copying, printing, or editing). Initial launch will support open-passwords; permissions follow.
More from Flint PDF
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Built browser-side, share the same editor.
Edit
Change what's on the page.
Organize
Rearrange or combine pages and files.
Merge PDF
Combine multiple PDFs into a single document.
Split PDF
Cut a PDF into one or many smaller files.
Reorder PDF Pages
Drag pages into the order you actually want.
Rotate PDF Pages
Spin selected pages 90°, 180°, or 270° in one click.
Delete PDF Pages
Remove pages from a PDF — single pages or whole ranges.
Export
Optimize or convert for sharing.