Why is my PDF so large?
Seven common causes of oversized PDFs, how to spot each one, and how to fix it.
Key facts
- Images cause most oversized PDFs — usually scans or phone photos at far higher resolution than needed.
- Text is tiny: a page of plain text is typically 2–20 KB.
- Repeated editing can leave old versions of content inside the file (incremental saves).
- Fonts, embedded attachments, metadata and thumbnails add smaller amounts.
1. High-resolution scans
Scanning at 300–600 DPI in colour produces 1–5 MB per page. For reading and normal printing, 150 DPI is plenty and grayscale is enough for text. Fix: compress the scan.
2. Photos straight from a phone camera
A 12–48 MP photo pasted into a document keeps its full resolution even when shown at thumbnail size. Fix: image re-encoding at Recommended typically saves 80%+.
3. Slides and designs exported to PDF
Presentation and design apps often embed every background image at original resolution, sometimes several times.
4. Incremental saves
Some editors append changes to the end of the file instead of rewriting it, so deleted pages and replaced images are still inside. Fix: our lossless cleanup rebuilds the file and drops unreachable objects.
5. Embedded fonts
Full font files (especially CJK fonts) can add several MB. Most exporters subset fonts; if yours doesn't, re-export with “subset fonts” enabled.
6. Attachments and multimedia
PDFs can carry attached files, audio or video. Remove them in your PDF editor if they aren't needed.
7. Metadata, thumbnails and editing data
XMP metadata, page thumbnails and application-private data (like PieceInfo) are invisible but add up. Our default cleanup removes them.
Frequently asked questions
What is a normal size for a PDF page?
Text-only: 2–20 KB. Text with a few graphics: 20–100 KB. Grayscale scan at 150 DPI: 50–150 KB. Colour photo page: 200 KB–1 MB.
Does converting to PDF/A reduce size?
No — PDF/A requires embedding all fonts and often increases size.
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