PDF encryption
Set an open password (and a permissions password) on a PDF, restricting copying, modification and printing
先说清楚：本页用 RC4-128，不是 AES-256
本页采用 PDF 标准安全算法 RC4-128（V2/R3）——Adobe Acrobat、WPS、macOS 预览、各手机阅读器都能正常打开与解密， 日常保密（合同、报表、内部资料、防止随手翻到）完全够用。 但 RC4 是较老的算法：若文件高度机密且需长期保管，建议用 Adobe Acrobat 的 AES-256 等专业加密，本页的产物可先用「PDF 去密码」工具（输入本页设的密码）去掉后再转专业加密。
把要加密的 .pdf 文件拖到这里，或点击选择
纯本地处理、文件不出本机；超过 100MB 建议先用「PDF 压缩」减小体积
4～128 个字符；建议 12 位以上、混用大小写字母与数字
两次必须完全一致
用于日后修改权限或移除加密；忘记它就无法改权限
提示：加密全程在本机完成，常见文件几秒完成；几百页或含大量图片的文件可能需要十几秒。完成后自动下载新文件，原文件不会被改动。
PDF 加密的适用场景与效果边界
产物是什么样。加密后的 PDF 与原文件内容一致（文字层、矢量、图片都保留），只是加了一层标准加密：填了打开密码，任何阅读器都要先输密码才能打开；「PDF 去密码」工具输入同一个密码即可还原为无密码版本，内容与版式不变。
权限限制是「防君子」。权限预设（禁止复制 / 禁止修改 / 仅打印等）只对遵守 PDF 标准的阅读器生效——部分开源阅读器可以忽略限制，所以它适合日常防误操作与防随手复制，不适合保护绝密内容。
已经有密码的 PDF。想换密码或改权限，先用本站「PDF 去密码」输入原密码去掉加密，再回本页重新设置——去密码必须知道原密码，忘了打开密码的文件任何工具都无法找回。
隐私与体积。加密全程在你的浏览器里完成：文件读取、加密、下载都发生在本机，本站任何时刻都没有获得你的文件（打开开发者工具 Network 面板可核验全程零上传请求）。纯本地处理没有服务器限制，只受本机内存约束；超过 100MB 的 PDF 建议先用「PDF 压缩」减小体积再加密。
FAQ
No. With an open password set, every reader requires it before showing the file; leave the open password empty and the file opens without one, governed only by the permissions. There is also a permissions password covering changes or removing the encryption; left empty it equals the open password.
The page uses the PDF standard security algorithm RC4-128 (V2/R3), which Adobe Acrobat, WPS, macOS Preview and phone readers all open and decrypt normally. It is enough to keep casual snoopers out, but RC4 is an older algorithm - for highly confidential files kept long-term, use professional AES-256 encryption such as Adobe Acrobat's.
No. Encryption happens entirely in your browser: reading, encrypting and downloading all take place on your machine - this site never holds your file at any moment. You can verify the zero uploads yourself in the developer tools Network panel. The encrypted result downloads straight to your machine and no copy is kept.
You can allow or forbid: copying text, modifying the document, adding annotations, filling forms, printing (including high-resolution printing), accessibility extraction and so on. Mind this: permission restrictions only bind readers that obey the PDF standard - some open-source readers simply ignore them, so treat them as keeping honest people honest, not as protection for top-secret material.
First use the PDF unlock tool on this site to remove the old encryption with the original password, then come back here to set the new password and permissions. Note that unlocking requires you to know the original password - for a file whose open password is forgotten, no tool (including this site's) can recover it.
Processing is purely local, so there is no server limit - only your machine's memory. For PDFs above 100MB we suggest running the PDF compressor first and then encrypting: the browser will be faster and steadier.