Where a 300 KB PDF limit comes up
300 KB sits between the tight 100 and 200 KB caps used for single certificates and the roomier 500 KB and 1 MB limits used for long documents. Forms tend to set it when they expect a document of a few pages that has been scanned rather than created on a computer. Typical examples:
- Domicile, income and category certificates with an attestation or verification page behind them
- Affidavits and undertakings on stamp paper, usually two or three pages with signatures and a notary's stamp
- Application forms you print, fill in by hand, sign and scan back, often with a photo pasted on the first page
- Mark sheets and certificates printed on both sides, scanned front and back
- Experience and relieving letters bundled with a salary certificate
These are examples, not rules. The limit belongs to the organisation running the form, so read its instructions for the exact size and format, and check whether 300 KB applies to each file or to all your uploads together.
What happens after you press Compress
The compressor works through a fixed order, from the least destructive option to the most, and stops as soon as the file is under 300 KB:
- Already small enough? A PDF that's 300 KB or less is handed back unchanged, with a note saying it doesn't need compressing.
- Recompress the images, gently. Photos and scans inside the PDF are re-encoded as JPEG and scaled so their longest side is at most 1,600 pixels. Text, fonts, links and form fields aren't touched.
- Recompress the images, harder. The same again at a lower JPEG quality, with a 1,100 pixel limit.
- Rebuild the pages as images. Each page is drawn as a JPEG picture at 150 DPI. If the file is still over 300 KB, it tries 120, 100, 85, 72, 60 and finally 50 DPI, skipping steps that clearly can't fit. If a low step fits with plenty of room to spare, it goes back and tries the sharper steps it skipped.
- Report the result. If even 50 DPI is too big, you get the smallest version it managed, with a warning that 300 KB wasn't reached.
The result card tells you which route was taken. Text kept selectable means one of the image passes was enough. Pages as images followed by a DPI figure means step 4 was needed. With a 300 KB target and a scan of more than a page or two, step 4 is common, so it's worth knowing what that DPI number means for your document.
Pages, DPI and readability at 300 KB
When pages are rebuilt as images, every page in the file gets the same DPI, so the number of pages decides how sharp the result can be. This is a rough guide for full A4 pages of printed text. Pages with plenty of white space, like most certificates, come out sharper; pages full of colour photos come out softer.
| Pages | Budget per page | Likely DPI | How it reads |
|---|---|---|---|
| 1 | 300 KB | 120–150 | Sharp: small print, stamps and signatures hold up when you zoom in |
| 2 | About 150 KB | Around 100 | Clear for normal-size print |
| 3–4 | 75–100 KB | 72–85 | Fine at normal zoom; small print and faint stamps soften |
| 5–6 | 50–60 KB | Around 60 | Body text readable, but footnotes and table figures may blur |
| 7 or more | Under about 45 KB | 50, or not reachable | Often too tight to stay readable: send fewer pages |
150 DPI is the highest the tool uses for page images, and it keeps small print crisp. At 72 DPI a page looks fine while the whole sheet fits on your screen, but small print turns fuzzy as soon as you zoom in. Treat 60 and 50 DPI as a last resort and read every line of the result before you submit it.
Scanning for a 300 KB target
A better starting file gives a sharper result at the same size. These habits matter more than any compressor setting:
- Don't scan at a higher resolution than you need. This tool never makes page images sharper than 150 DPI, and its image passes scale scans down to 1,600 pixels at most. A 600 DPI scan gives it almost nothing extra to work with at this size; it only takes longer to process. Scanning at 150 to 200 DPI is plenty.
- Use greyscale for black-and-white paperwork. Keep colour only where a stamp, seal or ink signature needs to show its colour.
- Keep phone photos straight and close. If your PDF was made from photos, a tilted shot with the desk around it wastes space. Retake or crop the photos, then rebuild the PDF with JPG to PDF on the Small file setting.
- Give each document its own file. Where a portal has one upload slot per document, separate files each get the full 300 KB instead of sharing it.
If you only have the PDF and some pages aren't needed, take them out before compressing. Split PDF has an Extract pages mode where you tap the pages to keep. Removing two unneeded pages from a five-page scan raises the budget for the rest from 60 KB to 100 KB a page.
What changes when pages become images
If the result card shows a DPI, the compressed file is a new PDF built from pictures of your pages. Each picture is drawn the way the page would print and placed at the original page size, so on screen it looks like the original. Underneath, a few things are gone:
- Text can't be selected, searched or copied, including any searchable layer added by OCR software.
- Links no longer open, and form fields can't be typed into. Entries you had already filled in are normally drawn into the picture, but check them.
- Bookmarks and document properties, such as the title and author, aren't carried over.
For a portal where an official simply views the document, none of this matters, which is why the step exists. Keep your original somewhere safe for everything else, and when you need another compressed copy, start again from the original rather than compressing the compressed file.
Certificates and affidavits stay on your device
An affidavit or domicile certificate usually carries your full name, address, ID number and signature. This page compresses it with code that runs in your browser: the file is read and rebuilt on your own phone or computer, and nothing is sent to KBSnap or anyone else. There's no account to create and no watermark on the result, so the only copy that goes anywhere is the one you upload to the form yourself.