How to Reduce PDF File Size for Free (Without Losing Quality)
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 ghostscriptgs -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.
How to tell what's inflating your PDF
Before reaching for a compressor, spend thirty seconds diagnosing the file. Divide the file size by the page count: a PDF containing only text and vector graphics rarely exceeds 100 KB per page, so anything approaching a megabyte per page almost certainly means embedded images. Two quick checks confirm it: try selecting text with your cursor — if nothing is selectable, each page is one big picture, which means you have a scan. Then zoom to 400%: real text stays razor-sharp, while image content turns soft and pixelated.
Don't overlook the cheapest savings of all: deleting pages nobody needs. Extracting the five relevant pages with our Split PDF tool often beats any compression algorithm, and it costs zero quality.
Scanned documents: the special case
A scanned PDF is a sequence of full-page photographs, which is why it responds so dramatically to image recompression — and why it's also the easiest to ruin. Reducing a 600 DPI scan to 150–200 DPI can cut the file by 80% or more, but small print — footnotes, contract clauses, serial numbers — degrades first. Two safe levers: convert color scans of black-and-white documents to grayscale (color data multiplies the size for no benefit), and stay at or above 200 DPI whenever the document contains fine text. After compressing, inspect the densest page at 100% zoom, not the cover. And if the file needs to go through OCR later, keep 300 DPI — text recognition accuracy drops sharply below that.
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.