Quick answer
A PDF is usually large because of high-resolution images or scans, fully embedded fonts, many pages, duplicated resources, or hidden data like thumbnails and editing history. Images are the most common cause. Analyse the file to see what's taking space, then compress images or remove what you don't need.
What makes a PDF large?
| Cause | How common | Fix |
|---|---|---|
| High-resolution images and scans | Very common | Compress PDF |
| Fully embedded fonts | Common | Compression with font subsetting |
| Colour scans of black-and-white pages | Common | Compress with grayscale |
| Many pages | Sometimes | Split or extract pages |
| Duplicate images on every page | Sometimes | Compression removes duplicates |
| Hidden data and layers | Occasionally | Flatten and clean metadata |
How do I find out what's making my PDF big?
Open Why is my PDF big? and drop in the file. You'll see how much space goes to images, fonts, page content and other data, plus suggestions for what would shrink it.
1. High-resolution images
Phone photos and scans are often saved at far higher resolution than a screen or printer needs. Recompressing them is the single biggest saving.
2. Embedded fonts
PDFs can embed entire font files so text looks right everywhere. Subsetting keeps only the characters actually used.
3. Colour scans
A colour scan of a black-and-white letter stores three times the data it needs. Grayscale or black-and-white saves a lot.
4. Lots of pages
Sometimes the file is simply long. Share only the pages that matter.
5. Duplicated resources
Logos or backgrounds repeated on every page may be stored many times. Good compression stores them once.
6. Hidden data
Thumbnails, form data, comments and editing history add weight. Flattening and cleaning metadata removes them.
Frequently asked questions
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