How to Compress a PDF to 100 KB (or Any Exact Size)
If you've ever tried to upload a PDF to a government portal, a job application, or an exam registration form, you've probably hit a message like this: "File must not exceed 100 KB."
Your scanned document is 2 MB. The form won't budge. And every compressor you try gives you three vague choices — low, medium, high — none of which tells you what size you'll actually end up with. So you compress, download, check the size, go back, try a different setting, download again. Sometimes four or five rounds of that.
There's a better way to do this, and it doesn't involve uploading your documents to anyone's server.
Why "low / medium / high" presets don't work for size limits
Most PDF compressors are built around quality presets, not size targets. A "medium" preset applies the same compression settings to every file — but the output size depends entirely on what's in your PDF. A two-page text document and a twenty-page scan of photographs will come out wildly different at the same setting.
When a portal says "under 100 KB," you don't care about presets. You care about one number. The tool should take that number and work backwards.
What actually happens when you target an exact size
The honest way to hit a byte target is trial and error — done by the software instead of by you. Docexp's exact-size PDF compressor runs a binary search on JPEG quality: it renders your pages, tries a quality level, checks the resulting size, then narrows up or down until the output lands at or just under your target. If quality alone can't get there, it steps the rendering resolution down — but never below the page's own natural pixel density, because past that point text turns into illegible mush (we learned that one the hard way and put a floor on it).
Two honest caveats, because compression that pretends to be magic isn't doing you any favors:
- Pages become images. To recompress a PDF this aggressively in the browser, each page is re-rendered as a JPEG. The file looks the same, but you can no longer select or search the text inside it. For a form upload, that almost never matters. For a document you'll keep editing, it does.
- Some targets genuinely aren't reachable. A dense 30-page scan will not become a legible 50 KB file, no matter which tool you use. When that happens, the tool tells you so and gives you the smallest legible version it could make — instead of silently handing you a blurry file that gets your application rejected.
Step by step
- Open the Compress PDF to exact size tool.
- Drop in your PDF. It never leaves your device — the compression runs as JavaScript in your own browser tab, which you can verify yourself by watching the Network tab in your browser's developer tools. Nothing gets sent anywhere.
- Type the size limit from your form — say, 100 KB.
- Click compress and download the result. The file will be at or under your number.
That's the whole process. No account, no watermark, no "3 free compressions per day."
If your upload is a photo, not a PDF
Exam and visa portals often have separate limits for photos and signatures — "photo: 20–50 KB, signature: 10–20 KB" is a common pattern. The same exact-size approach works there too: the image version of the compressor takes a JPEG or PNG and a KB target and does the same search on quality (and, for images, dimensions — shrinking a standalone image is normal and expected, unlike shrinking a PDF page).
When you don't have a hard limit
If nobody gave you a number and you just want the file smaller for email, the exact-size tool is overkill. The regular PDF compressor is the simpler pick — same in-browser processing, same privacy, just without the byte-target search.
One last tip that saves more space than any compressor: if your PDF came from scanning, check whether your scanner app has a "document" or "black and white" mode. A grayscale scan at 150 DPI is often a tenth the size of the full-color 600 DPI default — and then you may not need to compress at all.