How to use the Compress PDF tool
- Choose your PDF and read the box at the top: it explains how this compression works and what you give up.
- Pick a level: Smallest, Balanced or Better quality, or Custom to set resolution and JPEG quality yourself.
- Press Compress PDF and watch the page-by-page progress. You can press Stop at any time.
- Compare the sizes. If the result is smaller and still looks good, download it; otherwise keep the original.
Worked example: a scanned US Letter page at each level
scan.pdf is a scanned document on US Letter paper, 612 x 792 points. Here is what each level does to every page before it is saved as a JPEG:
- Smallest (72 DPI, JPEG 50): each page becomes a 612 x 792 pixel picture.
- Balanced (110 DPI, JPEG 65): 934 x 1,210 pixels, sharp enough to read on screen.
- Better quality (150 DPI, JPEG 80): 1,275 x 1,650 pixels, a better choice for printing.
The pages of the new file stay 612 x 792 points, so they print at the same size. The tool then shows the real before and after sizes; the saving depends on the scan, so judge by those numbers.
What this compression really does
Server-based tools can rewrite a PDF internally, recompress embedded images and drop unused data while keeping text as text. A browser tool without that engine cannot, so this one takes the honest route: each page is rendered to a picture at the DPI you choose, encoded as a JPEG at the quality you choose and placed in a new PDF. For scanned paperwork, which is already a picture, that can cut the size by 50 to 90 percent.
The costs are real. Text becomes part of the image, so it can no longer be selected, searched or read aloud, and sharp vector lines become pixels. Links, bookmarks and form fields are dropped. Fine print gets fuzzier at low settings. Never throw away the original.
When it helps and when it does not
It helps with scans, photo albums and slide decks full of pictures. It often makes things worse for ordinary text documents exported from Word or a browser, because such PDFs are already tiny and a picture of a page is larger than the text it replaces. When that happens the tool says so and shows the larger number rather than pretending. Balanced uses 110 DPI and JPEG quality 65, a sensible choice for reading on screen; use Better quality if you plan to print.
Your files stay on your device
Pages are drawn by pdf.js in your browser, encoded to JPEG by your browser and assembled into a new PDF by a background worker. Your document never leaves your device, so there is no queue, no server copy and no deletion policy to trust.
Frequently asked questions
Why did my PDF get bigger?
It was probably already efficient text and vector content. Re-drawing it as pictures is larger. Keep the original in that case.
Will I still be able to select and search the text?
No. After this compression each page is a picture, so text can no longer be selected or searched.
Which level should I use?
Balanced for most scans. Smallest for email limits. Better quality when you will print or need to read small text.
Is it as good as Acrobat or other desktop compressors?
No. Those can recompress images while keeping text. This tool trades text for pictures, which works well for scans but not for everything.
Can I compress a PDF with hundreds of pages?
Yes. Pages are processed one at a time with a progress bar, so the tab stays usable, though very large files need enough free memory.