How to Compress a PDF Without Losing Quality

A PDF that won’t attach to an email is one of those small, recurring annoyances. The fix is compression — but “compress” gets thrown around as if it’s one button that always works. It isn’t. Knowing what compression changes is the difference between a crisp 2 MB file and a blurry mess. I’ve squeezed thousands of PDFs down for email and uploads, and here’s how I do it without wrecking quality.

What “compressing a PDF” actually changes

The single most useful thing to understand: most of a PDF’s size is images, not text. Text and vector graphics are tiny. A scanned page or an embedded photo is huge. So PDF compression is really image compression — it downsamples pictures to a lower resolution and re-encodes them more efficiently.

That tells you two things:

• A text-only PDF (an exported document, a report) is already small. Compressing it barely helps, and that’s fine.
• An image-heavy PDF (a scan, a portfolio, a slide deck) is where compression pays off — sometimes shrinking the file by 80–90%.

Method 1: On a Mac (Preview, offline)

macOS can compress PDFs without any download:

1. Open the PDF in Preview.
2. Choose File → Export.
3. In the Quartz Filter dropdown, pick Reduce File Size.
4. Save.

The catch: Apple’s built-in “Reduce File Size” filter is aggressive and can make images too soft. If the result looks rough, the better move is a custom Quartz filter with a gentler resolution (around 150 DPI). You create one in the Mac’s ColorSync Utility, and it then appears in that same Export dropdown. It’s a five-minute, one-time setup that gives you reliable, offline compression for good.

Method 2: On any platform (Ghostscript, offline + scriptable)

If you want repeatable, offline compression with real control, Ghostscript is the tool the pros quietly use:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.5 \
   -dPDFSETTINGS=/ebook \
   -dNOPAUSE -dBATCH -dQUIET \
   -sOutputFile=compressed.pdf input.pdf

The key dial is -dPDFSETTINGS:

/ebook is my default — it’s the best balance of size and clarity for anything that’ll be read on a screen.

Method 3: Online (fast, any device)

When I’m not at my own machine, a web compressor is the quickest route: open it, drop the PDF in, pick a compression level, download. It works the same on phones and Chromebooks. The trade-off is the usual one — your file is uploaded to a server.

When compression won’t help

• The PDF is already mostly text — there’s almost nothing to compress.
• The images are already low-resolution — squeezing them further just adds blur.
• You need print quality — don’t drop below 300 DPI.

In those cases, if the file is still too big to email, don’t fight it: upload it to cloud storage and share a link instead. (That’s also the right answer for very large files in general — see our guide on reducing PDF size for email.)

My quick rule of thumb

For everyday “make this emailable” jobs, I reach for /ebook in Ghostscript or a 150 DPI custom filter in Preview. Both are offline, repeatable, and keep text razor-sharp while knocking image-heavy PDFs down to a fraction of their size. Start there, check the result on screen, and only go lower if you truly need to.