How-to
How to compress a PDF under 100KB
6 min read · Updated 29 August 2026
Upload limits like 100KB, 200KB or 1MB turn up constantly — government portals, university applications, job forms, visa submissions. They're often stricter than anything technical requires, and there's rarely any guidance on how to meet them.
The first useful step is figuring out why your file is large, because the fix is completely different depending on the answer.
Two kinds of large PDF
Scanned documents. Every page is a photograph. A phone-scanned page at full resolution can be 2–5 MB on its own. This is where nearly all oversized PDFs come from, and it compresses enormously.
Text documents. A PDF exported from Word or Google Docs is mostly text instructions and embedded fonts. A 30-page text document is often under 500 KB already. These barely compress at all, because there's little redundancy to remove.
Knowing which you have saves a lot of frustration. Try selecting text in your PDF: if you can highlight words, it's a text document. If the cursor just drags a box, it's a scan.
Getting a scan under 100KB
Scans compress well because image data is the entire file. In practice:
- A single-page ID scan can usually reach 100 KB with visible but acceptable quality loss
- A two-page document is achievable but tight
- Ten pages under 100 KB is not realistic — that's 10 KB per page, well below legibility
If you're being asked for ten scanned pages under 100 KB, check whether the limit is per file. It usually is, and splitting the document into separate uploads solves it.
Practical order of operations
Try these in sequence and stop when you're under the limit:
1. Rescan at a lower setting. The most effective fix by far, and the one people skip. Most phone scanner apps default to maximum quality. 200 DPI is plenty for text; 300 DPI is archival overkill for a form. Rescanning at 200 DPI in greyscale can cut the size by 80% before you compress anything.
2. Convert colour to greyscale. A black-ink document scanned in colour stores three channels of data to represent grey. Greyscale drops roughly two-thirds of that with no visible loss on text.
3. Crop the margins. Phone scans often include desk around the page. Cropping to the page reduces pixel count directly.
4. Then compress. Use Compress PDF and step down through the quality levels, checking legibility each time. Go one level at a time rather than jumping to maximum.
Why compression sometimes makes files bigger
A genuinely counterintuitive result: run a text-only PDF through an aggressive compressor and the output can be larger than the input.
This happens because aggressive compression usually works by rendering each page to an image and compressing that image. For a scan, that's fine — it was already an image. For text, you've converted crisp vector letterforms into a photograph of letterforms. JPEG is bad at sharp black-on-white edges, so it needs a lot of data to store them, and you end up with a bigger file that also can't be searched or copied from.
If your PDF is text and you need it smaller, the honest answer is usually that it's already near its floor. Options: remove images, subset the fonts, or split it into parts.
Checking the result
Before you submit anything:
- Read the smallest text. Look at footnotes, reference numbers, signatures. That's where artefacts appear first.
- Confirm it still opens. Some aggressive tools produce files that fail in strict readers.
- Check text is still selectable if it was before. If not, the tool rasterised your document, and anything relying on text extraction on the other end will fail.
Common limits
| Where | Typical limit | Realistic approach |
|---|---|---|
| Indian government portals | 100–200 KB | Greyscale, 200 DPI, single page per file |
| Job application forms | 1–2 MB | Standard compression is usually plenty |
| Email attachments | 10–25 MB | Rarely an issue unless scanned |
| University applications | 2–5 MB | Compress lightly, keep it readable |
When a portal rejects a file without saying why, size is the usual culprit — but check the page-count and format rules too. Many accept only single-page PDFs regardless of size.
Frequently asked questions
Why is my PDF so large?
Almost always because it's a scan. Each page is stored as a photograph, and a phone scan at full resolution can be several megabytes per page. PDFs exported from word processors are mostly text and font data and are usually far smaller to begin with.
Does compressing a PDF reduce its quality?
For scanned documents, yes — compression works by storing image data less precisely, and at aggressive settings you'll see artefacts around text. For text-based PDFs there's little to compress, and aggressive tools often make things worse by converting text into images.
Can I compress a PDF without losing quality?
Lossless compression exists — it removes duplicate objects, unused resources and inefficient encoding — but typically saves only 5–15%. Large reductions on a scanned document always involve discarding image detail.
How do I get a PDF under 100KB for a government portal?
Rescan at 200 DPI in greyscale rather than colour, crop away any margin captured around the page, and then compress. If the document is more than two pages, check whether the limit applies per file — splitting into separate uploads is usually allowed and far easier than crushing everything into one.
Why did compressing make my PDF bigger?
Because the file was text, not images. Aggressive compressors render each page to a picture and compress that, and JPEG handles sharp black-on-white text badly. You get a larger file that has also lost selectable text. If your PDF is text-based, it's probably already close to its minimum size.