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How to compress a PDF to 100KB

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Government and university portals routinely cap PDF uploads at 100KB, 200KB, or 2MB, and a scanned document sails past all three. A ten-page scan at 300 DPI is commonly 15–40MB, so this is not a small adjustment.

Understanding why the file is large tells you how to shrink it. In almost every case the answer is images: a scanned PDF is a stack of photographs, and the text you see is pixels rather than characters. Compressing the images is therefore the whole job, and text-only PDFs exported from Word barely shrink because there is nothing image-shaped to remove.

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Step by step

  1. Work out whether your PDF is a scan

    Try to select text in a PDF reader. If you can, it is a text PDF and already small — anything large about it is embedded images or fonts. If you cannot, it is a scan, and image compression will make a large difference.

  2. Remove pages you do not need to submit

    If the form asks for one page of a statement, split that page out first. Nothing shrinks a document like not including it.

  3. Rescan or re-export at a lower resolution

    This is the step that actually works, and it is worth being blunt: no browser-based tool re-encodes the images inside a PDF. Rescanning at 150–200 DPI instead of 600 cuts the data roughly sixteen-fold with no visible loss on screen or in ordinary print.

  4. If you cannot rescan, use a desktop tool

    For a scan you only have as a finished PDF, genuine image re-encoding needs something like Ghostscript on your own machine. That is an honest limitation of doing this in a browser tab.

  5. Confirm the smallest text is still readable

    Zoom to 100% and read the finest print on the page. A file that meets the limit but cannot be read will be rejected on review, which costs more time than starting again.

Things worth knowing

  • 100KB is very tight for a multi-page scan. If your document runs to several pages, expect to reduce resolution rather than rely on compression alone.
  • Be sceptical of any browser tool promising large PDF compression — most simply re-save the file and report the incidental difference as a saving.
  • Text-based PDFs are already efficient. If yours is only text and still large, the cause is usually embedded fonts or an oversized logo image.

Frequently asked questions

Why will my PDF not go below a certain size?

Because you have reached the floor for its content. Once images are compressed and downsampled, what remains — fonts, vectors, document structure — cannot be reduced further without removing content. For a multi-page scan, that floor may simply be above 100KB.

Does compressing a PDF make the text blurry?

Real text in a PDF is vector font data and is unaffected — it stays sharp at any zoom. Text inside a scanned image is pixels and will soften at aggressive settings. Which one you have determines how careful you need to be.

Is my document uploaded to compress it?

No. The PDF is parsed and rewritten in your browser, so it never leaves your device. That matters for the bank statements and identity documents most often subject to these limits.

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