缩小 PDF 文件体积：选一档清晰度（高清 / 标准 / 极限）或自定义渲染倍数与 JPEG 质量，逐页重新渲染后组装成新 PDF。页面尺寸保持不变，压缩前后大小直接对比。Shrink a PDF's file size: pick a quality preset (High / Standard / Maximum) or customize render scale and JPEG quality. Pages are re-rendered one by one and rebuilt into a new PDF with the same page size; before/after sizes shown side by side.
原理是把每一页转成图片再装回 PDF：扫描件、图片型 PDF 效果最好；文字型 PDF 压缩后文字不可选中复制，且若原文件已优化过、可能压完反而变大——此时页面会如实提示。加密或损坏的 PDF 无法处理。Each page is rasterized to an image and rebuilt into a PDF: best for scanned/image PDFs. Text in the output is no longer selectable, and an already-optimized PDF may grow larger — the page will tell you honestly if that happens. Encrypted or damaged PDFs cannot be processed.