What reaching 100 KB changes in a PDF

Set 100 KB as the target and the engine works down to it in steps, stopping at the first result that fits rather than padding the file back out.

It is the pictures inside the PDF that shrink: they are downsampled a step at a time until the file fits. Text typed into the document stays text while that is enough to reach the target. Ask for a size downsampling cannot reach and the pages are rendered to images instead, which makes the size but ends the text layer.

Files are processed on our servers, not in your browser. The upload and the result are both permanently deleted within 1 hour, no backups and no copies kept.

No watermark, and no account needed to use it. 2 files a day at up to 50 MB each, sent singly or together; signing in is free and raises each file to 100 MB.

Working at the readable limit

1. 1

   Decide what the document really is

   Ask first whether the pages are typed matter or pictures. Scanned paperwork survives 100 KB well. Pages that are mostly photographic do not, and knowing which you have saves a wasted upload.

2. 2

   Aim at the number, not below it

   Select 100 KB rather than something smaller on the theory that smaller is safer. There is no margin to win here, and every kilobyte you give up comes out of how clearly the page reads.

3. 3

   Inspect it at full size

   Enlarge the output until one page fills your screen, then try reading the footnotes, the small print and anything handwritten. Those go first, and judging the file from a thumbnail will mislead you.

The floor for a scan you can still read

100 KB is the smallest target that still hands you a scanned page you can sit and read. The evidence is a three-page scan that began at 13.2 MB and came back at 96 KB with its wording still clear on screen. Below this point, words that exist only as pixels begin to soften. Photographs behave differently, and the second section explains where they stop working.

Why a page of print survives at 100 KB

Embedded pictures account for 70 to 95 per cent of what a PDF weighs. Shrinking the document therefore means reducing those pictures: encoding them more harshly, then storing them at fewer dots per inch than the scanner originally produced.

Printed characters tolerate that better than you might expect, because they are high-contrast shapes with nothing subtle in them. Taking a 300 DPI scan down to screen resolution removes detail your eyes were never using. That is why the three-page example above arrives at 96 KB and still reads cleanly.

Where 100 KB breaks down: photographic pages

The 8.9 MB file built from full-page images is the warning case. It already falls to 82 KB when asked for 150 KB, so reaching 100 KB is never the problem. The problem is what it costs: mottled skin tones, banding across flat areas and a general muddiness a thumbnail hides and a full-screen view does not.

So if your document is really a set of photographs, use the 200 KB target, where that same file settles at 181 KB and holds visibly more of what the camera recorded. Keep 100 KB for paperwork and leave it alone for pictures.

What stays sharp whatever you ask for

Not everything in a PDF is at risk. Words typed into the document, along with lines, boxes and logos drawn as vectors, are never turned into pixels during compression. They display and print at full sharpness at 100 KB exactly as they would at 2 MB, and you can still select and copy them.

That matters when you are deciding whether to compress at all. A ten-page document of pure text occupies 19 KB before anything touches it, so a 100 KB target is beside the point. If your file came out of a word processor rather than a scanner, check its size first, because it is very likely far below the cap already.

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