Why Is My PDF So Large? 5 Causes and How to Fix Each One

A two-page document should be a few hundred kilobytes. So why is yours 20 MB? PDFs balloon for a handful of predictable reasons — and once you know which one you’re dealing with, the fix is usually quick.

1. It’s a scan

The most common cause by far. A scanner doesn’t store text — it stores a photograph of every page, often at 300–600 DPI. Ten scanned pages can easily outweigh a thousand pages of real text.

Fix: re-encode the page images. Run the file through Compress PDF with Strong mode, which re-encodes each page as an optimized image. Scans routinely shrink by 70–90%.

2. Oversized photos pasted into the document

A phone photo is 3–10 MB. Paste four of them into a report and export to PDF, and the full originals usually ride along — even if they’re displayed two centimetres wide.

Fix: compression re-encodes embedded images at a sensible size. If you’re building the document from photos in the first place, JPG to PDF keeps things lean from the start.

3. Embedded fonts — multiplied

Each embedded font adds anywhere from a few KB to over a megabyte (CJK and decorative fonts are the heavy ones). Documents assembled from multiple sources can carry a dozen full font files, many of them duplicates.

Fix: Light compression rewrites the file’s internal structure and removes redundant objects without touching quality — text stays crisp and selectable.

4. Pages nobody needs

Cover sheets, blank scanner pages, the 40 appendix pages after the 2 pages you actually need to send.

Fix: delete the dead weight, or extract just the pages you need into a new file. Fewer pages is the one size reduction that costs nothing in quality.

5. Revision history and leftover data

PDFs support incremental saving: some editors append every edit to the end of the file instead of rewriting it, so the file grows with every save — and old, “deleted” content is still in there.

Fix: any full rewrite of the file discards the accumulated history. Light compression does exactly that as a side effect.

Find your culprit in 10 seconds

Can you select the text in your PDF? If you can’t, it’s a scan — expect big savings from Strong mode. If you can, the weight is in images, fonts or history — start with Light mode and keep your text selectable. Either way, you can check the result instantly: the compressor runs entirely in your browser, so there’s no upload, no queue and no file-size cap.

Facing a hard limit like “max 100 KB” on an application portal? There’s a dedicated guide and tool for that.