How to Compress a PDF: Quick Re-save vs. Rasterize (and When Each Fails)
The two real ways to shrink a PDF, why they work completely differently, and how to pick the right one instead of guessing.
"Compress this PDF" means two completely different things depending on what's actually inside the file — a text document and a scanned image-heavy PDF don't shrink the same way, and using the wrong method either does nothing or destroys something you needed.
Quick re-save: lossless, modest savings
This mode re-saves the PDF's internal structure more efficiently without touching a single pixel or letter — text stays selectable, images stay exactly as they were. It works well on documents that were already reasonably built, but if the original file has genuinely large embedded images, this mode alone won't shrink much, because it isn't re-encoding those images at all.
Rasterize & compress: big savings, one real tradeoff
This mode renders every page as an image and re-compresses it — which can shrink a scanned document dramatically, since scanner output is often needlessly high-resolution. The real tradeoff: text becomes part of the image, so it's no longer selectable, searchable, or copyable afterward. This is the right tool for a bulky scan, the wrong one for a document someone needs to search or copy text from.
How to tell which one your PDF needs
If you can select and copy text from the PDF today, it's a real text document — try Quick re-save first. If the PDF is a scanned image (you can't select text, or it looks like a photo of a page), Quick re-save won't help much and Rasterize is the one that will actually shrink it.
When neither mode is enough
A PDF full of already-highly-compressed photos (not scanner output) has little room left to shrink either way — the images are already near their practical size limit. In that case, the honest fix isn't a better compression setting, it's reducing the number or resolution of the images before they're placed into the PDF in the first place.
Quick tips
- Try Quick re-save first — it's non-destructive, so there's no downside to trying it before Rasterize.
- If you rasterize a document and later need the text searchable again, you'll need to go back to the original file — rasterizing isn't reversible.
- A PDF that's still large after rasterizing at a reasonable resolution is probably carrying more pages or more detailed scans than compression alone can meaningfully reduce.