Why Your PDF Won’t Compress (and What Actually Works)
A PDF is a container. Whether it can be made smaller depends entirely on what is inside it. Once you know that, you can predict the result before you start — and avoid tools that “compress” by turning your text into a blurry picture.
What makes a PDF big
| Inside the PDF | Typical effect on size | Can it shrink? |
|---|---|---|
| Photos and scanned pages (JPEG) | Large — often most of the file | Yes: downsize and re-compress the images |
| Text and vector drawings | Small | Very little |
| Embedded fonts | Small to medium | Only by removing or subsetting fonts |
| Black-and-white scans (CCITT/JBIG2) | Already very small | Rarely |
| CMYK or JPEG 2000 images | Medium to large | Not safely in a browser |
The honest way to compress
Our Compress PDF finds the JPEG images inside the file, scales oversized ones down (to at most 2,000, 1,600 or 1,100 pixels on the long side) and re-encodes them at a lower quality. Text, fonts and vector graphics are not touched, so text stays sharp and selectable. It reports how many images it changed and keeps the original if compression would not help.
Some tools reach dramatic sizes by turning every page into one flattened image. The file gets smaller, but text can no longer be selected, searched or read by screen readers. Check by trying to select a word in the result.
If your PDF barely shrinks
- Mostly text? It is probably already small. Check the size: a 30-page text document is often under 1 MB.
- Too big for an upload limit? Split it into parts, or remove pages you don’t need with Delete PDF Pages.
- Scanned at very high resolution? Rescan at 150–200 DPI for documents, or 300 DPI only when fine print matters.
- Lots of photos from a phone? Compress the photos first with Compress Image, then build the PDF with JPG to PDF.