Why is my PDF so large? The common causes
In short
Almost always it's the images: high-resolution scans or phone photos placed straight into the PDF. Text takes up very little space. Compressing the images, as the tool below does, usually solves it.
Do it right here
The causes, most common first
- High-resolution scans. A scanner set to 600 DPI colour produces pages of several MB each. For documents, 200 to 300 DPI is plenty.
- Phone photos. A 12-megapixel photo is 3 to 5 MB; ten photos make a 30 to 50 MB PDF.
- Colour scans of black and white documents. Colour triples the amount of data with no benefit for reading.
- Fully embedded fonts. Design programs sometimes embed entire fonts instead of just the characters used.
- Duplicate images. PDFs merged from several sources can contain the same logo dozens of times.
How to see what takes up space
Divide the file size by the number of pages. Over 500 KB per page almost certainly means large images. Under 100 KB per page, the document is already compact and compression will gain little.
What to do
- Try Compress PDF at the Recommended level. The text stays selectable.
- If it's a scan and still large, choose Strong or a target size.
- Remove unnecessary pages with Delete PDF pages.
- Next time, scan at 200 to 300 DPI, in black and white or greyscale for documents.