How much can a PDF be compressed?

Scanned and photo-heavy PDFs often shrink by 50–90%. Text-only PDFs are already compact and may only shrink by 5–20%.

Is it safe to compress PDFs online?

Reputable services delete files after a few hours, but your file is still uploaded to someone else's server. For contracts, IDs, medical or financial documents, prefer a method that runs on your own device.

Why is my compressed PDF blurry?

The compression level was too strong and images were reduced to a very low resolution. Go back to your original and use a medium ('recommended') level instead.

How to Compress a PDF (Free, Any Device)

Before you start

Keep the original. Compression can’t be undone.
Know your target. Email limits are usually 20–25 MB; many upload portals want under 2–10 MB.
Check why it’s big. A scanned document shrinks a lot; a text-only file won’t. See Why is my PDF so large?

Option 1: Online (any device, fastest)

Open a free online PDF compressor. Adobe, Smallpdf, iLovePDF and others offer one.
Upload your PDF.
Choose Recommended / Medium compression.
Download the result and open it to check readability.

Privacy tip: avoid uploading sensitive documents such as passports, bank statements or medical records. Use one of the local options below.

Option 2: Mac (built-in, free, offline)

Open the PDF in Preview.
Choose File > Export…
In Quartz Filter, select Reduce File Size.
Save with a new name.

The built-in filter can be very aggressive and make scans blurry. If the result looks bad, use an online tool at a medium setting instead.

Option 3: Windows (offline)

Windows has no built-in PDF compressor, but you have free options:

Recreate the PDF from the source. In Word, choose File > Save As > PDF and select Minimum size (publishing online).
LibreOffice Draw (free): open the PDF, then File > Export as PDF and set JPEG quality to about 75% and “Reduce image resolution” to 150 DPI.
Adobe Acrobat (paid): File > Save as Other > Reduced Size PDF.

Option 4: iPhone or Android

Use your phone browser with an online compressor, as in Option 1.
Or rescan the document at a lower quality. Many scanner apps have a “file size” or “quality” option.

Option 5: Advanced — Ghostscript (free, any OS)

If you’re comfortable with a command line, Ghostscript gives excellent results locally:

gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dNOPAUSE -dBATCH -sOutputFile=small.pdf input.pdf

Use /screen for smallest, /ebook for balanced (≈150 DPI), /printer for high quality.

Still too big?

Split the PDF into several parts.
Send a share link (Google Drive, OneDrive, iCloud, Dropbox) instead of an attachment. See PDF too large to email.