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Compress PDF online, free

Shrink file size by re-encoding images and rewriting the structure.

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Compress PDF makes a PDF smaller by re-encoding the JPEG images inside it at a lower quality and resolution, then rewriting the file so unused objects and duplicated structure are dropped. With the three standard levels, text, links and form fields are left as they are, so the result still reads, searches and prints like the original. A fourth level, Flatten to images, trades that for the largest saving.

The whole job runs in your browser with JavaScript. The file is never uploaded, so there is no transfer to wait for and nothing stays behind when you close the tab. Files up to 100 MB each, twenty at a time. When you compress several at once, each comes back as its own PDF and you can download them together as a ZIP.

How much you save depends on what is in the file. A scanned document or a photo-heavy brochure can shrink a great deal. A PDF that is mostly text has almost nothing to give up, and images stored in lossless formats are left untouched by the three standard levels. With those levels, if the rewritten file would not be smaller, the tool hands back your original unchanged and tells you so.

How to use Compress PDF

  1. 1Click Select files, or drop your PDFs onto the page. Use Add more files to include others.
  2. 2Choose a compression level: Light, Balanced, Strong, or Flatten to images. Balanced is selected by default.
  3. 3Click Compress. The progress bar names each image as it is recompressed, or each page as it is rendered if you chose Flatten to images.
  4. 4Read the note showing the size before and after, then click Download to save the compressed PDF, or Download all as ZIP if you compressed several.

Frequently asked questions

How much smaller will my PDF get?
It depends on how much of the file is images. Scans and photo-heavy documents often shrink a lot, while a text-only PDF may barely change. After compressing, the tool shows the size before and after, and with Light, Balanced or Strong, if no saving was possible it returns your original file unchanged and says so.
Will the text still be selectable and searchable?
Yes, with Light, Balanced or Strong. Those levels only touch the images, so text, links and form fields stay exactly as they were. Flatten to images is the exception: it renders every page to a picture, so text can no longer be selected, searched or read by a screen reader.
What is the difference between the compression levels?
Each level shrinks embedded JPEG images to a maximum size and re-encodes them at a set quality: Light keeps images up to 2400 px on the longest edge at 85 percent quality, Balanced 1600 px at 68 percent, and Strong 1100 px at 50 percent. Flatten to images renders each page at 120 dpi as a JPEG at 60 percent quality and rebuilds the PDF from those pictures.
Is my file uploaded to a server?
No. The images are decoded, resized and re-encoded on your own device using your browser's built-in JPEG support. Nothing is sent to FreeAIPDF or anyone else.
Why did my file not shrink at all?
The standard levels only re-encode JPEG images in RGB or grayscale. Images stored in lossless formats, CMYK images, transparency masks and very small images are skipped, and a PDF that has already been optimized has little left to give. For a scanned document, Flatten to images usually gives a much larger saving.
Does it work on scanned PDFs?
Yes. If each scanned page is stored as a JPEG, Light, Balanced and Strong re-encode it and keep any existing text layer. Scans stored in other formats, such as black-and-white CCITT or JBIG2 images, are skipped by those levels. Flatten to images works on any scan because it renders the page, but it discards the text layer, so if you need the scan to stay searchable, run OCR PDF on the result afterwards.

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