If you compressed a PDF and the size barely changed, the cause is usually one of a few common culprits. Here's why each happens and how to fix it.
Cause 1 — Scanned images are already compressed to low resolution
Most of a PDF's size comes from embedded images (especially scans), not the text. If your scanning app already dropped the JPG quality significantly before creating the PDF, there's little left to compress further. In that case, check the resolution/quality setting at scan time rather than pushing compression harder afterward.
Cause 2 — Fonts are fully embedded
If a document has custom or non-Latin fonts fully embedded, the text portion can be larger than expected. PDFs exported from design software often embed the entire font. Many compressors shrink images but leave embedded fonts untouched, which is why even a text-heavy document sometimes doesn't shrink.
Cause 3 — Too many pages
If a document runs hundreds of pages, the absolute file size stays large even at maximum compression. Beyond compressing, consider splitting out just the pages you need or deleting unnecessary ones first — the size drop from that is often much bigger than compression alone.
Cause → fix, at a glance
| Symptom | Cause | Fix |
|---|---|---|
| Barely shrinks after compression | Images already low-resolution | Check original scan resolution |
| Large even with just text | Embedded fonts | Minimize embedded fonts |
| Still tens of MB after compression | Too many pages | Split or delete pages, then compress |
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