Why Is My PDF So Big?
A one-page file at 40 MB isn't magic — it's almost always one of four causes. Find yours, pick the right fix.
Cause 1 — scanned images inside (the usual suspect)
A scanner saves each page as a full-resolution photo. At 300 DPI, one A4 page is roughly 8–15 MB before compression. Thirty scanned pages later, your "document" is a photo album. Fixes: rescan at 150 DPI if the text still reads clearly, scan in black-and-white for text, or compress the PDF to a target size after the fact.
Cause 2 — embedded fonts (whole families of them)
Some exporters embed every font they touched, including full character sets for languages the document never uses. A text-only PDF should be tens of kilobytes per page; if it's megabytes, fonts are the reason. The fix belongs in the source: re-export with subsetting enabled (Word, LaTeX and InDesign all do this by default — "disable subsetting" is the setting to uncheck).
Cause 3 — embedded attachments and print data
PDFs can carry hidden cargo: source files attached by the author, prepress data, or full editing histories. The page you see might be 200 KB while the file hauls a 30 MB embedded original. Re-exporting from the source, or printing to PDF, strips the cargo — with the trade-off that the text becomes flattened.
Cause 4 — the images were never downscaled
A 48-megapixel phone photo placed at 6 cm wide still stores all 48 million pixels. Publishing tools that "place" images instead of exporting them at display resolution produce this constantly. Fix at the source with downsampling on export; fix after the fact with image-target compression.
Quick diagnostic
| Symptom | Likely cause | Cheapest fix |
|---|---|---|
| Scanned document, huge | Cause 1 | Target-size compress |
| Text-only, still MB-sized | Cause 2 or 3 | Re-export from source |
| Only some pages bloated | Cause 4 on those pages | Re-export or compress |
| Same PDF grew after edits | Cause 3 (history) | Save As / re-export |
When to fix it where it stands
If the source document is gone (a PDF someone sent you), re-exporting isn't an option — that's exactly the case the compressor here handles: state the size you need, get the best quality that fits, all in the browser. Need to keep only part of it? Split first, then compress — fewer pages is free compression.