How to compress a PDF offline

You need a PDF under an email or upload limit, but the document is confidential — or you are on a train with no signal. These methods shrink PDFs without an internet connection and without sending the file anywhere.

Quick answer

Open LocalDocu’s Compress PDF page once while online. After that it works offline: select the PDF, choose Balanced (keeps text selectable) or Maximum (smallest file), and save. The file never leaves your device.

Method 1: LocalDocu in the browser (Windows, Mac, Linux, Android, iPhone)

1. Visit localdocu.org/compress-pdf once with a connection so the app is cached.
2. Select or drop your PDF (up to 40 MB per file in the browser).
3. Choose Balanced first; switch to Maximum with a lower quality target if you need it smaller.
4. Compare the before and after size, then save the result.

Method 2: Preview on a Mac

Open the PDF in Preview, choose File → Export, and set Quartz Filter to “Reduce File Size”. It is fast but often aggressive — images can become very blurry, so check the result.

Method 3: Ghostscript (command line, all platforms)

If you are comfortable with a terminal, the free Ghostscript tool compresses offline with presets such as /screen (smallest), /ebook (balanced) and /printer (higher quality):

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

Which PDFs compress best?

• Scanned documents and photo-heavy PDFs usually shrink the most.
• Text-only PDFs are often already small; expect modest savings.
• If you must keep text searchable, avoid modes that turn pages into images (LocalDocu’s Maximum, Ghostscript’s /screen on some files).

Questions about compressing PDFs offline

• Compress a PDF now
• How offline mode works
• Split PDF
• All guides