🗜️ PDF 压缩Compress PDF

使用说明与常见问题How-to & FAQ

「PDF 压缩」是什么？What is the Compress PDF tool?

在浏览器里减小 PDF 体积：重新压缩文件中的照片（降低分辨率和 JPEG 质量）并优化文件结构，文字保持可搜索；也可整页栅格化获得最大压缩率，会实时显示压缩前后大小。Shrink PDFs in your browser — re-compress embedded photos (lower resolution and JPEG quality) and optimise the file structure while text stays searchable, or rasterize whole pages for maximum compression. Before/after sizes are shown.

如何使用「PDF 压缩」？How do I use the Compress PDF tool?

在「PDF 压缩」中，按需设置「方式」、「压缩程度」等选项，然后点击「压缩并下载」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 Compress PDF: Set "Mode", "Level", then click "Compress & 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.

压缩原理是什么？How does the compression work?

PDF 体积大多来自照片。“压缩图片”模式会找出文件中的 JPEG 照片，按所选程度降低分辨率并重新压缩，同时用对象流优化文件结构；文字、矢量图形保持不变、仍可搜索复制。Most PDF weight comes from photos. Compress images finds the JPEG photos inside the file, downsamples and re-compresses them to the chosen level and optimises the structure with object streams; text and vector graphics are untouched and remain searchable.

为什么有的 PDF 几乎压缩不了？Why do some PDFs barely shrink?

如果文件主要是文字、矢量图形或已经压缩过的图片，可压缩空间很小；CMYK、带特殊解码参数的图片会被跳过以免颜色出错。结果不比原文件小、或只小了不到 1% 时，工具会提示并不提供下载。图片外层套有 ASCII85/ASCIIHex 编码的也会正常处理。Files that are mostly text, vector graphics or already-compressed images have little to gain, and CMYK or specially-decoded images are skipped to avoid color errors. If the result isn't smaller, or is less than 1% smaller, you'll be told and no download is offered. Images wrapped in ASCII85/ASCIIHex encoding are handled too.

加密的 PDF 压缩后还有密码吗？Does an encrypted PDF keep its password?

没有。输入密码打开后，压缩结果保存为不加密的 PDF；如需密码保护，请再用本站的“PDF 加密”工具设置。No. After you open it with its password, the compressed copy is saved without encryption; use this site's Protect PDF tool to add a password again.

“整页栅格化”有什么代价？What's the cost of Rasterize pages?

每页会被渲染成一张 JPEG 图片再重新组成 PDF，扫描件通常能压缩得很小，但文字不能再选择、搜索，链接和表单也会丢失。Each page is rendered to a JPEG and rebuilt into a PDF. Scans often shrink a lot, but text can no longer be selected or searched and links and forms are lost.

“也压缩无损图片”要不要勾选？Should I tick "convert lossless images"?

截图、图表、文字图片等无损（PNG 类）图片转为 JPEG 后可能出现模糊或噪点，默认不处理；照片类的无损图片勾选后可以明显减小体积。Screenshots, charts and text images stored losslessly may look blurry or noisy as JPEG, so they're skipped by default; tick it when the lossless images are photos to save a lot of space.

加密的 PDF 可以处理吗？Can it handle password-protected PDFs?

可以。如果 PDF 需要打开密码，会提示你输入；只有权限限制（无打开密码）的文件会自动打开。输出文件不再带密码，如需加密请使用“PDF 加密”工具。Yes. If the PDF needs an open password you'll be asked for it; files with only permission restrictions open automatically. The output is not password-protected — use the Protect PDF tool if needed.

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 压缩」免费吗？需要注册吗？Is the Compress PDF free? Do I need an account?

「PDF 压缩」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 Compress PDF is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.