What is PDF compression?

PDF compression makes a PDF file smaller so it is easier to email, upload or store. Most of the size of a large PDF usually comes from images, such as scanned pages or photos saved at a much higher resolution than a screen or printer needs. Scaling those images down and saving them as JPEG shrinks the file a lot, while text and drawings stay exactly as they were.

Tool description

This tool compresses one PDF at a time. It shows every page as a thumbnail with all pages selected, so you can compress the whole PDF right away. To compress only some pages, clear the selection and tick the pages you want, or type them as page numbers and ranges. Pick a compression level, compress, compare the original and compressed file sizes, then download the result.

Features

  • Compresses the whole PDF, or only the pages you pick
  • Three compression levels, from best quality to smallest file
  • Scales large images down and saves them as JPEG
  • Keeps text sharp and selectable, and keeps fonts, links, bookmarks and form fields
  • Shows the original size, the compressed size and how much you saved
  • Opens any page in a full-size preview

How it works

The PDF never leaves your device: it is read, compressed and saved in your browser.

Each image on the chosen pages is scaled down to at most the level's resolution for the page it is on, then saved as JPEG:

Level Resolution JPEG quality
Low 200 DPI 85%
Medium 150 DPI 70%
High 96 DPI 50%

An image is only replaced when the JPEG is smaller than the original. When you compress only some pages, an image that also appears on a page you didn't pick, such as a logo on every page, is left as it is, so the other pages look exactly the same as before.

Some images are always left as they are, because JPEG can't show them the same way: CMYK images, black-and-white scans stored as 1-bit images, JPEG 2000 images, images with a limited color palette, and the masks that make parts of other images transparent.

The whole file is then cleaned up without any loss of quality: objects that nothing uses any more, such as leftovers from earlier edits, are removed, uncompressed data is compressed, and the document structure is packed into compressed object streams.

Tips

  • Scanned documents and PDFs full of photos shrink the most. A PDF that is mostly text has little to gain.
  • If the compressed file isn't smaller, try a higher compression level.
  • The thumbnails show the original pages. Open the downloaded file to check the image quality before you delete the original.
  • Encrypted and password-protected PDFs can't be compressed.