100 KB: room for a readable page or two
A 100 KB limit is a common middle ground on document uploads. It comfortably holds one scanned page at a resolution where small print stays readable, and two or three pages of a typed document. Mark sheets, transfer certificates, experience letters and fee receipts usually fit without trouble.
A PDF exported from Word or a government website is often already under 100 KB, or gets there through the lossless step, so its text can still be selected. A scanned PDF is a picture of the paper and is usually much larger; it is redrawn to fit.
Keeping a mark sheet readable at 100 KB
Mark sheets are the hard case: small digits in narrow columns, often on a coloured security background. Two things help. First, ticking black and white removes the background tint, which leaves more of the 100 KB for the digits themselves. Second, a straight, cropped scan means the space is spent on the sheet rather than on the desk underneath.
The result shows the DPI and JPG quality the tool chose. Around 100 DPI and above, printed text of normal size stays clear on screen. If the tool had to go well below that, the PDF has more pages than 100 KB can hold clearly.
What DPI means here
DPI (dots per inch) is how many pixels are used for each inch of the page when it is redrawn. An A4 page at 100 DPI is about 830 x 1,170 pixels, enough for a form reviewer to read on a screen. Halving the DPI quarters the number of pixels, which is why a long document has to drop to a low DPI to fit a small limit. The tool picks the highest DPI that still fits with a good JPG quality, rather than squeezing quality to the bottom.
Other limits
For a single small certificate, compress PDF to 50 KB explains what to expect; for longer documents, compress PDF to 200 KB. Any other number works on compress PDF, and photos have their own compress image to 100 KB.
Built on two open-source projects that run in your browser: qpdf, compiled to WebAssembly, for the lossless rewrite, and Mozilla's PDF.js to redraw pages when that is not enough.