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PDFパスワード保護・暗号化および解除ツール
PDFパスワード保護・暗号化および解除ツール
本ツールは100%クライアントサイド（ブラウザ内）で動作します。写真、動画、音声、PDFファイルが外部サーバーにアップロードされることは一切なく、お使いの端末のメモリ内で安全に処理されます。
コアアーキテクチャ & 計算式
Encrypted PDF = AES-128/256(Document Bytes, User Password, Owner Password, Permission Flags)
The PDF specification defines a security handler that encrypts the document's content streams using either RC4 or AES algorithms. The User Password gates document opening, while the Owner Password controls granular permission flags (print, copy, modify, annotate).
ベストプラクティスとガイドライン
- Always Set Both Passwords: The User Password prevents unauthorized opening, while the Owner Password prevents permission changes. Setting only one leaves a security gap — a document with only an Owner Password can still be opened by anyone.
- Use Strong, Unique Passwords: PDF encryption strength is directly tied to password entropy. Use at least 12 characters combining uppercase, lowercase, digits, and symbols. Avoid dictionary words or predictable patterns.
- Test Before Distributing: After encrypting, always open the resulting PDF in a separate viewer (Adobe Reader, Chrome, Firefox) to verify the password prompt appears correctly and permissions are enforced as expected.
- Keep a Backup of the Original: PDF encryption is a one-way operation on the output file. If you lose the password, the encrypted file cannot be recovered. Always maintain an unencrypted backup in a secure location.
よくある質問 (FAQ)
Can I remove a password from a PDF if I know the password?
Yes. The 'Unlock' mode loads the encrypted PDF using your provided password, then saves a new copy without any encryption. This effectively strips all password protection from the document.
Is the encryption secure enough for sensitive documents?
The pdf-lib library applies standard PDF encryption as defined in the PDF specification. For maximum security, use long, complex passwords and consider additional measures like secure file transfer for distribution.
Will encryption change the visual content of my PDF?
No. Encryption wraps the existing content streams in a cryptographic envelope. The text, images, fonts, and layout remain pixel-identical — only the access control layer changes.
Are my passwords stored or transmitted anywhere?
Absolutely not. Passwords exist only in your browser's local JavaScript memory during processing. They are never written to disk, sent over the network, or logged in any capacity.