为 PDF 添加密码
加密你的 PDF，使其只能用你设置的密码打开。
工作原理
1. 上传你的 PDF。2. 输入密码并确认。3. 下载——文件将被加密（AES-256），只能用该密码打开。
我的密码会被发送到别处吗？
不会——加密完全在你的浏览器中完成。你的文件和密码永远不会离开你的设备。
如果我忘记密码怎么办？
无法找回——加密是真实的，因此忘记密码意味着任何人（包括我们）都无法打开该文件。请把密码保存在安全的地方。
使用的是哪种加密方式？
AES-256，当前 PDF 的标准加密强度，通过广泛使用的开源 qpdf 引擎在你的浏览器中运行完成。
Does this work on a mobile browser?
Yes — it's a regular web page, not an app, so it works the same way in a mobile browser as on desktop. Tap to pick the file, set a password, and download the encrypted result — the encryption still happens entirely on your device.
Does this restrict printing or copying, not just require a password to open?
No — it's a single password that's required to open the file. Once someone has entered it, they can print, copy, and edit like normal; there's no separate owner password or permission controls that limit what an already-authenticated reader can do. Worth knowing anyway: those "disable printing/copying" options other tools offer are only honored by well-behaved PDF readers — anyone can strip them by printing the file to a new PDF.
What makes a good password for this?
Something reasonably long that isn't a guessable word — not your birthday, not "password123". We only require 4 characters minimum so we don't block anyone, but since there's no permission system backing this up, that password is the only thing standing between someone and the file. Treat it like a real password.