PDF パスワード保護

Everything You Need to Know About Protect PDF

How PDF password protection works in your browser

1. Upload the PDF you want to protect. OmniPDF reads it into memory with pdf-lib — no bytes are sent to a server. The file is available for encryption the moment it finishes loading.
2. Enter an open (user) password. Anyone who opens the finished PDF will be prompted for this password. Choose something long enough to resist brute-force but short enough to share securely with intended recipients.
3. Optionally add an owner password. This second password bypasses all restrictions you set, letting you or authorized admins print, copy, or edit without limits. If you leave it blank, the open password also serves as the owner password.
4. Toggle permission flags to decide what recipients without the owner password can do: allow or deny high-resolution printing, text copying, and content modification. These flags are stored in the PDF header and respected by standard viewers.
5. Click Protect & Download. pdf-lib applies AES-128 encryption, embeds the permission flags, and triggers a browser download. Close the tab when done — the encrypted bytes exist only in your download folder, not on OmniPDF infrastructure.

Technical security, privacy, and why no registration is required

Password protection in OmniPDF is computed entirely inside your browser tab using pdf-lib's encryption layer. The open password, owner password, and permission flags are applied to an in-memory ArrayBuffer before the download fires. No intermediate encrypted copy is staged on OmniPDF application servers, which means an attacker cannot intercept a half-encrypted document from our side of the wire. HTTPS still protects the delivery of the JavaScript bundle itself, but the sensitive password material and document bytes never leave your machine for this operation.

Accounts are unnecessary because the encryption step is stateless: you supply a password, pick permissions, and get a file. That keeps the surface area small — there is no OmniPDF credential database tied to your document passwords for adversaries to target. You remain responsible for strong password hygiene, distributing the password through a separate channel, and storing the protected PDF on hardware that matches your organization's data-classification policy. AES-128 PDF encryption is strong for most business workflows, but high-assurance environments may require certified redaction or additional controls beyond a viewer-enforced password.

Five scenarios where local PDF password protection helps

• HR teams emailing offer letters with salary details to candidates, protecting the file so only the recipient can open it without uploading sensitive compensation data to a cloud conversion service.
• Lawyers sending draft settlement agreements to clients and restricting copying so terms cannot be copy-pasted into competing bids before both parties sign.
• Finance departments distributing monthly board packs as encrypted PDFs, setting the owner password so auditors can later print high-resolution copies while distribution copies restrict editing.
• Teachers sending student reports home as password-protected PDFs where the password is the student ID, keeping records accessible to parents but closed to unintended recipients.
• Freelancers locking final deliverable PDFs before invoice payment, allowing clients to preview at low resolution but requiring the owner password to print or extract high-quality assets.