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How to Compress a PDF to 100 KB: 4 Practical Methods

Need a PDF under 100 KB for an upload form? Four ways to shrink it with an online tool, Preview, Acrobat or Ghostscript, plus fixes if it still won’t fit.

By Mechanic Tech. Solution · Published 8 November 2026 · Updated 8 November 2026 · 4 min read · 914 words

Illustration of a large PDF document with an arrow pointing to a much smaller PDF document, labeled compress a PDF to 100 KB

Some job portals, exam registrations and government forms accept documents only up to 100 KB, and a scan taken with a phone camera can be far larger. A target-size compressor is the simplest fix. If a file still won’t fit, lower its image resolution or remove pages. This guide covers four ways to do it.

Key Takeaways

  • Images, not text, usually make PDFs large, so compression works mainly by lowering image resolution and quality.
  • In a test of three synthetic files with a 100 KB target, an online compressor shrank a one-page scan from 1.10 MB to 94.1 KB, but could not get a text-only file or a six-page scan under 100 KB.
  • Acrobat and Ghostscript give finer control over image settings, while Preview offers one preset filter.
  • Reopen the compressed file and confirm that names, numbers and stamps are still readable before you upload it.

The four methods at a glance

Method Works on How you control size
Online compressor Any modern browser Target-size presets
Preview Mac One preset filter
Acrobat Windows and Mac Image downsampling and compression
Ghostscript Windows, Mac, Linux Resolution presets

Method 1: Use an online compressor with a target size

Compress PDF files online is PDF Karigar’s own tool. After you add a PDF, you choose a compression level (Light, Recommended, Strong or Extreme) or tap a target size of 100 KB, 200 KB, 500 KB, 1 MB or 2 MB. You can also type your own size in KB or MB. With a target size, the tool tries quality settings from best to lowest and keeps the best one that fits.

  1. Open the tool and choose your PDF.
  2. Tap 100 KB.
  3. Select Compress PDF.
  4. Download the result and check its size.

PDF Karigar’s privacy policy says files are processed in your browser and not sent to its servers, which matters for ID cards and certificates.

What a test showed

Three synthetic PDFs, generated for this guide, were run through the live tool on 2026-11-08 with a 100 KB target:

Test file Original Result
Text-only PDF 107.7 KB 106.1 KB, not under 100 KB
One-page colour scan 1.10 MB 94.1 KB
Six-page colour scan 6.62 MB 200.4 KB, not under 100 KB

The one-page scan fit, and its text stayed readable. For the other two files the tool said it couldn’t get under 100 KB and showed the smallest size it could reach. This matches the tool page’s own note that text-only PDFs are already compact and the big savings come from photos and scans. Six pages of scans stayed above 100 KB even at the smallest possible size. Each file was run once, and results vary with file type and content.

Screenshot of the PDF Karigar result screen for a six-page scan: 6.62 MB reduced to 200.4 KB, with a message that the file couldn't get under 100 KB and the smallest possible size is 200.4 KB
The tool’s result screen for the six-page scan: 6.62 MB to 200.4 KB, short of the 100 KB target.

In the six-page case, splitting the file or removing pages is the next step.

Method 2: Use Preview on a Mac

  1. Open the PDF in Preview.
  2. Choose File > Export.
  3. Open the Quartz Filter menu and select Reduce File Size.
  4. Click Save, preferably under a new name.

Apple’s Preview guide offers this filter and a few image options rather than a size target, and warns that the result may look worse than the original. Check the file size afterwards.

Method 3: Use Adobe Acrobat

On Windows, choose Menu > Save as Other > Optimized PDF. On a Mac, choose File > Save as Other > Optimized PDF. Adobe’s guide says the Mobile setting downsamples colour and grayscale images more than Standard, and Custom lets you adjust the Images panel. Check the size after each save.

Method 4: Use Ghostscript for batch jobs

Ghostscript is free command-line software for shrinking many files. The Ghostscript documentation lists 72 dpi for colour images under the /screen preset and 150 dpi under /ebook, and warns that presets can make output worse than the input.

gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -o output.pdf -f input.pdf

Try /ebook first, then /screen if the file is still over 100 KB. Always start from the original file.

If the file is still over 100 KB

Change the document before compressing again:

Keep the original file in case you need to start again.

Check the file before you upload

Open the compressed PDF at 100 percent zoom. Names, ID numbers, dates and stamps should be easy to read. Then check the size, and leave a few KB of margin in case the portal measures it differently.

Try it on your file

Ready to get under 100 KB? Open the 100 KB PDF compressor in your browser and run your file through it.

Written by Mechanic Tech. Solution, the company behind PDF Karigar. Source details and test results are from 2026-11-08. Spotted an error? Tell us through our contact page or at [email protected]. Learn more about PDF Karigar.

Sources

Open the 100 KB compressor