A PDF can be large for several different reasons, and the right fix depends on the cause. Here are five practical ways to reduce file size, and when each one helps.
1. Downsample embedded images
The biggest wins usually come from images. Reducing their resolution and re-compressing them can cut a file by 70–90% with little visible difference at normal viewing sizes.
2. Re-save with efficient compression
Even text-only PDFs can shrink a little when re-saved with modern stream compression that removes redundancy. This is lossless — nothing is degraded.
3. Remove pages you don't need
If you only need to share two pages of a 50-page document, extract just those pages. It's the simplest size reduction of all.
4. Scan smarter
If you control the scan, use 150 DPI and grayscale for documents. This produces far smaller files than 600 DPI colour, with no real loss for text documents.
5. Strip metadata and extras
Author info, thumbnails, and revision history add weight. A good optimizer removes these automatically.