Password-protecting a PDF before you email it is the difference between “attached” and “exposed” if the message is forwarded or the mailbox is breached. This tool builds a PDF that any standard reader refuses to open without your password — genuine PDF standard encryption, applied on your device.
What “locked” means here — the full, honest picture
The output file is encrypted with the PDF standard security handler (the same mechanism Adobe Acrobat applies): without the password, its contents are unreadable, not merely hidden behind a polite request. Your password is never transmitted anywhere — the encryption happens in this page.
One trade-off, stated plainly because it matters: producing an encrypted file in a browser requires rebuilding the document, so each page is rendered at a high 200 DPI and placed inside the protected PDF as an image. Appearance is preserved; text selectability and search are not. Treat the locked file as the delivery copy and keep your original as the master. The permission checkboxes (printing, copying, modifying) are requests that compliant readers honour — they are enforced by reader software, which is true of permissions in every PDF tool, including Acrobat's.
Choosing a password that holds
Length beats cleverness: four random words beat “P@ssw0rd”. Never reuse your email or banking password on a document. And send the password by a different channel than the file — a text message, not the same email — otherwise the lock protects nothing.
Private by design
Like every CalcViso file tool, this one runs entirely in your browser. The file you choose is read by this page, processed on your device, and offered back as a download — it is never uploaded to a server, never stored, and never seen by anyone else. Close the tab and it is gone from memory.
Worked example
Use the sample: lock the 2-page sample PDF with the password “test123”, download it, and open it — your PDF reader will refuse to show anything until you type the password. That refusal is the encryption working, not a viewer setting.
How to use this tool
- Drop the PDF you want to protect (keep the original somewhere safe).
- Type a password — twice — and choose the permissions readers should allow.
- Press Lock PDF with password.
- Download locked.pdf and open it once to confirm it demands the password.
- Send the file and the password by different channels.
Forgotten passwords are forever
There is no “forgot password” for a PDF — that is rather the point. This page cannot recover a locked file, and neither can we. If the document matters, store the password in a password manager at the moment you create it.