你有一份 PDF 格式的产品手册。第 1 页是一张你想发在聊天软件里的全页照片；第 4 页是一个带有小字体的规格表，适合放在 wiki 页面上。两页内容，两种不同的用途。 在此处打开 PDF，并在 Pages 字段中输入 1。设置按钮已显示为 JPG · 150 dpi，这非常适合发送到聊天的照片：在我们的测试中，一张充满照片的 A4 页面，在 150 dpi 的 JPG 格式下大小约为 0.25–0.5 MB，而 PNG 格式则为 3.5–4 MB。 现在处理表格。将数字改为 4，打开设置并选择 PNG；如果用户需要放大查看小字体，请选择 High (300 dpi)。切换格式会保留原有的 PDF 和分辨率设置，因此无需重新操作。PNG 以无损压缩方式存储绘制的像素，因此字母边缘和表格线条将保持清晰。对于纯文本页面，两种格式的大小相近，而在我们的 WebKit（Safari 的内核）测试中，PNG 文件甚至更小。 每一页将作为单张图像下载，文件名由原文件名和页码组成：例如 brochure-page-1.jpg 和 brochure-page-4.png。如果你选择了多个页面，它们将按文档顺序一起打包在一个 ZIP 文件中。底部的状态栏会告知你上一个文件所使用的格式和分辨率，即使在切换格式后，点击 Download again 仍可获取同一个文件。 无论哪种方式，你得到的都是一张白底的页面图片：图像中的文本无法选中，链接无法点击，表单字段也无法填写。PDF 在你的设备上读取，不会被上传。 我的指南通过实测文件大小对比了 JPG 和 PNG，并涵盖了分辨率、页面范围以及页面转换为图像后的变化。
You have a product brochure as a PDF. Page 1 is a full-page photo you want to post in a chat; page 4 is a spec table with small print that belongs on a wiki page. Two pages, two different jobs. Open the PDF here and type 1 into the Pages field. The settings button already says JPG · 150 dpi, which suits a photo for a chat: in our tests, an A4 page filled with a photograph came out at about 0.25–0.5 MB as a JPG at 150 dpi, against 3.5–4 MB as a PNG. Now the table. Type 4 instead, open the settings and choose PNG, and High (300 dpi) if people will zoom into the small print. Switching the format keeps your PDF and the resolution as they were, so there is nothing to redo. PNG stores the drawn pixels without lossy compression, so the edges of letters and table lines stay clean. For text pages the two formats come out close in size, and in our WebKit tests (the engine behind Safari) the PNG was even the smaller file. Each single page downloads as one image, named after your file and its page number: brochure-page-1.jpg and brochure-page-4.png. If you choose several pages, they arrive together in one ZIP, in document order. The strip at the bottom tells you which format and resolution the last file was made with, and Download again gives you that same file even after you have switched formats. Either way, you get a picture of the page on a white background: text in the image can't be selected, links don't work and form fields can't be filled. The PDF is read on your device and not uploaded. My guides compare JPG and PNG with measured file sizes, and cover resolution, page ranges and what changes when a page becomes an image.
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