PDF files have a way of ballooning to 50 MB when you need them to be 5 MB for an email attachment. The good news is that most PDFs are bloated by high-resolution images embedded inside them — compress those images and the PDF shrinks dramatically. Here are the free methods that actually work.

Why PDFs get large

Most PDF bloat comes from one of three sources:

High-resolution images: a PDF exported from Canva or InDesign at print quality embeds 300 DPI images. For screen viewing, 72–96 DPI is plenty.
Embedded fonts: PDFs embed full font files. A document using five custom fonts can add 2–5 MB of font data alone.
Scanned pages: a scanned PDF is literally a sequence of photos. Each page scanned at 600 DPI can be 2–3 MB.

Method 1: Compress images before creating the PDF

The cleanest approach is to compress images before they go into your PDF workflow. If you're assembling a PDF from screenshots or photos, run them through our Image Compressor first. JPEG at 80% quality reduces a 4 MB photo to 200–400 KB with no visible change on screen. Then combine the compressed images into a PDF — the result is already small.

Method 2: Use a free online PDF compressor

Several free online tools compress existing PDF files by downsampling their embedded images:

ILovePDF — free tier allows compression of PDFs up to 100 MB. Offers low, recommended, and extreme compression levels.
Smallpdf — free tier with daily limits. Good UI, handles scanned PDFs well.
PDF2Go — free, no daily limits. Slower than the alternatives.

Privacy caveat: these tools upload your PDF to their servers. For confidential documents, use a local method (see below).

Method 3: Mac Preview — Export with reduced file size

Mac's built-in Preview app can compress PDFs without any third-party software:

Open the PDF in Preview.
Go to File → Export as PDF.
Click Quartz Filter and select Reduce File Size.
Save the new file.

This method is aggressive — it downsizes images to 72 DPI. For a PDF you'll only ever view on screen or email, that's fine. For one you'll print or archive, use a less aggressive method.

Method 4: Adobe Acrobat Reader (free)

The free Adobe Acrobat Reader doesn't include compression, but the free Adobe Acrobat online tools (acrobat.adobe.com/compress-pdf) allow two free compressions per day without signing in. Results are good — Adobe's algorithm is well-tuned.

Method 5: Ghostscript (command line)

For power users or automated workflows, Ghostscript is the gold standard. It's free and open source. On Mac with Homebrew:

brew install ghostscript
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

The -dPDFSETTINGS flag controls compression: /screen for maximum compression (72 DPI images), /ebook for medium (150 DPI), /prepress for minimal compression (300 DPI, print quality).

How much can you compress a PDF?

A typical 10 MB PDF from Canva compresses to 1–2 MB with online tools. A scanned document at 30 MB can shrink to 3–5 MB. PDFs that are mostly text with no images barely shrink at all — they're already efficient. Expect 50–80% reduction for image-heavy PDFs, 10–30% for text-heavy ones.

After compressing: check quality

Always open the compressed PDF before sending. Aggressive compression can make small text unreadable or photographs visibly blocky. The right balance is the smallest file where everything still reads clearly at 100% zoom.