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.
When small savings are the right answer
A quick re-save that only shrinks a file by a few percent is not a failure — it is information. It means the PDF was already built efficiently, and the remaining bytes are real content, not waste. Chasing those last bytes with rasterize would cost you selectable text for almost no gain. Let the mode match the problem: structure problems get a re-save, oversized scans get rasterizing, and an already-lean document gets left alone.
For scans: fix orientation before you rasterize
Rasterizing bakes each page into pixels exactly as it currently lies — including sideways. If a scanned document has rotated pages, fix them with Rotate PDF first, then rasterize. Reordering matters less (page order survives rasterizing unchanged), but orientation, once rendered into an image, can only be fixed by rotating the image itself, which is a second lossy step for scanned content.
Aim comfortably under the limit, not at it
Most people compress a PDF because something rejected it: an email cap (25 MB is common), an upload form, a messaging app. Compress for the strictest limit you actually face and aim comfortably below it — mail servers and portals often count encoded size, which is larger than the file size on disk. If rasterizing at a sensible resolution lands you just under the cap, stop there; squeezing further costs visible quality for margin you do not need.
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.
- Keep an un-rasterized master of any document whose text matters; rasterize a copy for sending.
- Still huge after rasterizing? Lower the render resolution — for scans, resolution is the big lever, not quality.