無料ツール
選択したパスワードでのみ開けるようにPDFをパスワード保護 — 即座にダウンロード、アカウント不要。
使い方
3ステップでPDFを保護する
- 1
Upload your PDF
Drag and drop your PDF onto the tool or click to browse. The file loads in your browser — never sent to any server.
- 2
Set a password
Enter your chosen password and confirm it. Use at least 4 characters — longer passwords are stronger. The same password will be required to open the protected PDF.
- 3
Download the protected PDF
Click 'Download protected PDF'. mupdf applies AES-256 encryption in your browser and the protected file downloads immediately.
Signvoyを選ぶ理由
強力な暗号化、アップロード不要
AES-256 encryption
The tool uses mupdf's AES-256 encryption — the same standard used by governments and financial institutions — applied entirely in your browser.
Instant download
Encryption is applied by the mupdf WebAssembly module and your browser downloads the protected file immediately — no queue, no waiting.
Your file stays on your device
Everything runs locally. Your PDF and your password are never sent to any server — close the tab and both are gone.
よくある質問
よくある質問
- What happens if I forget the password?
- There is no recovery option — the encrypted PDF cannot be opened without the correct password. Store your password securely before downloading.
- What encryption standard is used?
- AES-256 (Advanced Encryption Standard with a 256-bit key), applied via mupdf compiled to WebAssembly. This is a widely accepted strong encryption standard.
- Will the protected PDF work in Adobe Acrobat?
- Yes — the password-protected PDF is a standard encrypted PDF that opens in Adobe Acrobat, Apple Preview, and most other PDF viewers when the correct password is entered.
- Can I remove the password later?
- Yes — use the free Unlock PDF tool. You will need to provide the current password to remove the protection.
もっと詳しく知りたいですか？ 完全ガイドを読む: PDFをパスワードで無料でオンライン保護する方法 →
署名の催促をやめよう
Signvoyを使って取引を成立させ、クライアントをオンボーディングし、契約書に署名している数千のチームに参加しましょう — より速く。
クレジットカード不要 · 永久無料プラン · 14日間プロトライアル