PDF Compression Levels Explained: Lossless, Balanced, Strong and Extreme
In this article
Every PDF compressor promises smaller files, but few explain what they actually do to your document. That matters: some methods leave the PDF untouched apart from its size, while others turn every page into a picture. This guide explains the four compression levels in the free PDF compressor, what each one changes, and how to pick the right one for your file.
Why PDFs are large in the first place
Text barely takes up any space in a PDF — a 50-page text report can be under 1 MB. Large PDFs are almost always large because of images: scanned pages, phone photos of documents, or high-resolution pictures in a brochure. Embedded fonts and inefficient internal structure add a little more. So the right compression method depends on what your PDF contains.
The four levels, explained
| Level | What it does | Text stays selectable? | Best for |
|---|---|---|---|
| Lossless | Rewrites the PDF’s internal structure more efficiently. Nothing visible changes. | Yes | Digital documents, forms, anything you must keep searchable |
| Balanced | Re-renders each page as a JPEG image at about 108 dpi, quality 72% | No | Scanned documents that need to stay easy to read |
| Strong | Page images at about 79 dpi, quality 55% | No | Scans that must fit an upload limit |
| Extreme | Page images at about 61 dpi, quality 42% | No | The smallest possible file, where readability is secondary |
Lossless: start here for digital PDFs
If your PDF was created from Word, a website or other software, try lossless first. Text, links and quality are unchanged. The saving is usually modest — often 5–30% — and some PDFs are already optimised. In that case the compressor keeps your original and tells you, rather than handing back a “compressed” file that is no smaller.
Balanced, Strong and Extreme: for scans and photos
These levels redraw each page as an image at a lower resolution and save it as a JPEG. For a scanned document this often cuts the size by 60–90%, because scanners usually save at far higher resolution than you need to read a page on screen. The trade-off is that the result is a picture of each page: you can’t select or search the text, and links stop working.
How to choose, in practice
- Digital PDF? Use Lossless. If it is still too big, the size is probably coming from images inside it — try Balanced.
- Scanned PDF? Start with Balanced and check that small print is still legible.
- Still over the limit? Try Strong, then Extreme. Zoom in to check the result before you submit it.
The compressor always shows the size before and after, so you can try levels one after another in a few seconds.
Hitting a specific upload limit
Government and exam portals often cap uploads at 100 KB, 200 KB, 1 MB or 2 MB. For very small limits on multi-page scans, compression alone may not be enough. Two things help:
- Remove pages you don’t need with the PDF splitter — blank backs of pages are common in scans.
- Scan at a lower resolution next time: 150 dpi in black and white is enough for most forms.
Our step-by-step guide to compressing a PDF to 100 KB covers this in detail.
Privacy
All four levels run in your browser. Your PDF isn’t uploaded anywhere, which makes the compressor safe for bank statements, ID documents and certificates. Password-protected PDFs need to be unlocked first with the PDF unlocker (you’ll need the password).
What to look for in any PDF compressor
- Clear levels that say whether text stays selectable.
- Before-and-after sizes, so you know whether it helped.
- Keeping the original when compression wouldn’t make it smaller.
- Where your file goes — browser-based processing means no upload.
For more background, see how to compress a PDF without losing quality.