🔐 PDF 加密Protect PDF with Password
给 PDF 设置打开密码（AES-256 加密），并可限制打印、复制文字、修改、批注、填写表单和页面重组；未填写权限密码时自动生成高强度随机密码，全部在本地完成，密码不会上传。Password-protect a PDF with AES-256 encryption and optionally restrict printing, copying, editing, annotating, form filling and page assembly. A strong random owner password is generated if you leave it blank. Runs locally — your password never leaves the browser.
使用说明与常见问题How-to & FAQ
「PDF 加密」是什么？What is the Protect PDF with Password tool?
给 PDF 设置打开密码（AES-256 加密），并可限制打印、复制文字、修改、批注、填写表单和页面重组；未填写权限密码时自动生成高强度随机密码，全部在本地完成，密码不会上传。Password-protect a PDF with AES-256 encryption and optionally restrict printing, copying, editing, annotating, form filling and page assembly. A strong random owner password is generated if you leave it blank. Runs locally — your password never leaves the browser.
如何使用「PDF 加密」？How do I use the Protect PDF with Password tool?
在「PDF 加密」中，按需设置「再次输入」、「加密算法」等选项，然后点击「加密并下载」按钮即可。支持拖放文件。加密的 PDF 选好后会先出现「打开密码」栏和「打开」按钮，输入密码点「打开」后再继续。In the Protect PDF with Password: Set "Confirm", "Algorithm", then click "Encrypt & download". Drag-and-drop files is supported. For an encrypted PDF, a Password field and an Open button appear after you choose it — enter the password and click Open first.
加密强度如何？How strong is the encryption?
默认使用 AES-256（PDF 2.0 标准，Acrobat X 及以后、主流浏览器和阅读器都支持）。真正保护内容的是打开密码，请使用足够长、不易猜到的密码。AES-256 is used by default (PDF 2.0 standard, supported by Acrobat X+, browsers and mainstream readers). The open password is what really protects the content, so make it long and hard to guess.
打开密码和权限密码有什么区别？Open password vs. owner password?
打开密码（用户密码）用于打开和阅读文件；权限密码（所有者密码）用于解除打印、复制等限制。权限密码留空时，工具会生成 18 位随机密码并显示一次，请自行保存。The open (user) password is needed to open and read the file. The owner password lifts restrictions such as printing or copying; if you leave it empty an 18-character random one is generated and shown once — save it yourself.
只限制权限、不设打开密码安全吗？Is restricting permissions without an open password secure?
不太安全。没有打开密码时，文件内容只是“请求”阅读器遵守限制，很多工具都能直接去除。保护机密内容请务必设置打开密码。Not really. Without an open password the restrictions are only a request to well-behaved viewers, and many tools can strip them. Always set an open password for confidential content.
忘记密码怎么办？What if I forget the password?
无法找回。AES 加密没有后门，本工具也不保存你的密码，请在加密前记好密码并保留未加密的原文件。It can't be recovered. AES has no back door and this tool never stores your password, so note it down and keep the unencrypted original.
文件会上传到服务器吗？Are my files uploaded?
不会。PDF 在你的浏览器里用 pdf-lib / pdf.js 处理，文件不会离开你的设备，关闭页面后不留存任何数据。No. The PDF is processed in your browser with pdf-lib / pdf.js; files never leave your device and nothing is kept after you close the page.
「PDF 加密」免费吗？需要注册吗？Is the Protect PDF with Password free? Do I need an account?
「PDF 加密」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Protect PDF with Password is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.