pdfpix

Compress PDF to 400 KB

or drop one here
Compression level
Target size
Choose a PDF file first.

400 KB is 409,600 bytes, and it is the size a multi page scan lands on when it has been compressed sensibly rather than aggressively. The bench did not measure a 400 KB target. The 500 KB target it did measure was met on 9 of 16 cases, and 400 KB is a little tighter than that.

How to compress a PDF to 400 KB

  1. Choose the PDF

    Press Choose a PDF, or drop the file on the page. The file is read in this tab and is not sent anywhere.

  2. The target is already set

    This page opens at 400 KB, so there is nothing to type. Pick a different level, or enter your own smaller number in KB, if you want another size.

  3. Press Compress

    Four methods race: copy the pages into a fresh file, re-encode the placed images, cut each embedded font down to the glyphs the pages draw, and, only when no other method reached the target, redraw the pages as images with the text kept on top.

  4. Read the check, then download

    Every candidate is opened again and its characters are counted against the source. The page shows the size, the method that won and the characters kept before it offers the download.

The four methods are described in full, with the measurements behind them, in how it works.

The multi page scan case

400 KB is a good number for four to eight scanned pages. That is 50 to 100 KB of image per page, which holds printed text, keeps a signature legible, and does not turn a stamp into a smudge. Below four pages you have room to spare; past ten it gets tight.

The compress tool works to the number you give it and reports the one it reached. If the result comes back at 380 KB against a 400 KB cap, the file has already found its own level and there is no reason to push further.

Colour is the lever nobody thinks of

A colour scan of a black and white document costs roughly three times what a greyscale scan of the same page costs, before any compression runs. Scanners default to colour because it is the safe choice, not because the document needs it.

If the paper is still on your desk, rescanning in greyscale at 200 or 300 dpi will beat any compression setting. If it is not, the image methods here do the same job after the fact, with less to work with.

Neighbouring targets

A 300 KB target is the next step down and is where single page certificates usually belong. A 500 KB target is the next step up and was measured on the public bench at 9 of 16 cases.

Pick the tightest cap you are actually asked for, then subtract a little. Upload forms that count kilobytes in thousands are stricter than their label, and a file aimed at 390 KB clears both readings without a second attempt.

Questions

Is 400 KB enough for an eight page scan?
Yes, at about 50 KB per page. Printed body text stays readable and signatures stay legible. Fine print and small handwriting start to soften, so check the page with the smallest type before you send it.
What is 400 KB in bytes?
409,600 bytes at 1,024 bytes to the kilobyte. A form counting in flat thousands caps at 400,000, which is 9,600 bytes tighter. The tool uses the binary reading, so aim at 390 KB when a form has already refused you once.
Will a 400 KB target keep my text selectable?
Yes. Text retention is checked on every candidate before it ships, with a floor of 98% of the non-space characters. On the published run every one of the 102 documents that carried text came back at 100%.
Should I compress to 400 KB or split the file instead?
Split it if the pages serve different purposes and the form accepts more than one upload. A four page file at 400 KB looks far better than a twelve page file at the same cap, because each page gets three times the budget.

The other pdfpix tools

All 30 of them run in a browser tab like this one. Each reads its own output back and checks it before offering the download, and none of them needs an account.

Where to go next