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How to compress a PDF to 300KB (free, online)

By LeDeuxions · 29 October 2026

You fill in the whole form, pick your file, and the upload box turns red: maximum file size 300 KB. Your scan is 1.8 MB. This is one of the most common walls on visa, exam and government portals, and the fix takes about a minute. Here is how to do it without installing anything, without signing up, and without handing your document to a stranger.

Why a form wants 300 KB

300 KB looks arbitrary, but it is a deliberate choice by the people who built the form. A portal that collects thousands of applications has to store and move every file people send it. Capping each upload keeps that manageable, and 300 KB is a sensible middle: big enough for a readable two- or three-page scan, small enough that a server is not buried under gigabytes of photos.

You will meet the same limit in a few other places — older email systems that reject large attachments, shared drives with tight quotas, and messaging apps that silently refuse anything over a certain size. Whatever the reason, the task is the same: get the file comfortably under the number without making it unreadable.

The fast way: compress to an exact size in your browser

Most compressors give you vague settings like "low, medium, high" and leave you guessing. The problem with a 300 KB limit is that you don't want smaller — you want as close to 300 KB as possible, because every kilobyte you keep is detail you keep. A target-size tool handles that for you: you type the limit, and it searches for the highest quality that still fits.

1. Open the 300 KB compressor. It is already set to 300 KB, so you don't have to type anything.
2. Drop your PDF onto the page. In browser mode the file stays on your computer — nothing is sent to a server.
3. Press compress. The tool tries a range of resolutions and settles on the sharpest one that lands under 300 KB.
4. Download and check. Open the result and make sure the important parts are still legible before you upload it.

Tip: aim a little below the limit — around 290 KB. Websites disagree about whether a kilobyte is 1,000 or 1,024 bytes, and a file that reads as 301 KB on one system reads as 294 KB on another. A small margin saves you a second rejection.

If your PDF is a scan or full of photos

Scanned pages and phone photos are where the megabytes hide. A single A4 page scanned in colour can be a megabyte or more on its own, because it is stored as a photograph, not as text. A few habits make a big difference:

• Drop pages you weren't asked for. Size is shared across pages. If the form wants "proof of address", it needs the page with your name on it, not all six pages of the statement. Fewer pages means more detail on the ones that count.
• Lose colour you don't need. A greyscale or black-and-white scan of a text document is often half the size of the colour version. Keep colour only where it carries meaning — a stamp, a photo, a signature in blue ink.
• Rescan at a lower resolution if you can. Many people scan at 600 dpi out of habit. For a document that will be read on screen, 150–200 dpi is plenty, and it starts the file at a fraction of the size.

Once the obvious bulk is gone, let the compressor do the last mile down to 300 KB.

If your PDF is mostly typed text

A PDF exported from Word or a web page stores its words as text, which is tiny — a ten-page report with no images might already be under 200 KB. When a text PDF is unexpectedly large, the weight is almost always one or two oversized embedded images: a logo saved at 4,000 pixels wide, or a photo pasted straight off a camera. Image-based compression would throw away the efficient text layer and could even make things worse. A high-quality compressor that resamples only the images while leaving the text alone is the better choice, and it usually reaches 300 KB with no visible change at all.

When it simply won't fit

Some files can't go under 300 KB and stay readable — fifteen pages of dense small print, for instance. Pushing the compression harder just turns letters into grey mush. When you hit that point, the honest options are better than a ruined file:

• Check whether the form accepts more than one file, and split the document across several uploads.
• Upload only the pages the form actually requires.
• Email or call the office. Most would rather receive a legible partial document than an unreadable complete one.

Frequently asked questions

That's the whole job: cut what you don't need, drop colour that adds nothing, and let a target-size tool find the sharpest version that fits. Ready when you are.