How do I get a PDF under 100 KB for an upload form?

Job portals, exam registrations, scholarship applications, visa and government forms: many of them accept a PDF only if it is under 100 KB, sometimes 200 KB or 300 KB. A one-page certificate scanned on a phone is often 1 to 3 MB, ten to thirty times too big.

Why the limit is so small

A portal that takes documents from hundreds of thousands of applicants has to store and review all of them. A 100 KB cap keeps that manageable and keeps uploads working on slow connections. The limit is not a judgement about your document; it is just the size the system was built for.

What makes a PDF heavy

A PDF that was typed on a computer is mostly text. Text is tiny: a page of it is a few kilobytes.

A scanned PDF is different. Each page is a photograph of the paper, and a photograph is made of millions of dots. A page scanned at 300 dots per inch in colour has about 8.7 million of them. That picture is almost the entire file.

So the way to make a scan smaller is to make that picture smaller: fewer dots per inch. The question is how far you can go before the text becomes hard to read.

How far down can you go?

Further than most people expect. For reading on a screen, 100 to 150 dots per inch is plenty for normal-sized text. We tested a one-page colour scan of an invoice at 970 KB: brought down to 54 KB, every line, including the small print in the table, was still readable.

Compress PDF to 100 KB works this way. It lowers the resolution of the pictures in steps and stops at the first step where the file is under 100 KB, so the result is only as soft as it has to be. Text that is real text, not part of a scan, is never turned into a picture and stays sharp.

When it will not go under 100 KB

Sometimes the file cannot get that small:

• Many pages. Ten scanned pages at 10 KB each is already 100 KB. Check whether the form wants every page. Often it asks for the first page of a certificate or one page of a mark sheet.
• Mostly text, fonts and drawings. A long report typed on a computer has little picture to shrink. The fonts and text themselves take room.

In both cases you are told the smallest size it reached rather than being handed a file that still fails. Then the fix is fewer pages: take out the ones you do not need with Organize PDF, or cut the document into parts with Split PDF if the form lets you upload several files.

100 KB is not always 100 KB

Some sites count a kilobyte as 1,000 bytes and others as 1,024. A file of 101,000 bytes is under the limit on one and over it on the other. The size you set here is counted as 1,000 bytes per KB, so a file that fits passes on both kinds of site.

A checklist before you upload

• Scan or photograph the page flat, in good light, filling the frame. A clear original compresses better and stays readable at a smaller size.
• Crop away the table or desk around the paper. Empty edges are still pixels.
• Upload only the pages the form asks for.
• Open the compressed file and read the smallest text on it before you submit.