Limits measured in kilobytes — 200 KB, 300 KB, 500 KB — turn up on government portals, exam and scholarship applications, and older HR systems. A document exported from Word fits easily. A phone scan usually doesn't: a single color photo of a page can be 2–4 MB on its own. Getting it small enough is possible, but it takes the right settings and sometimes a little trimming.
Turn the KB limit into MB
The Target size field in Compress PDF takes megabytes and counts 1 MB as 1,024 KB. Divide your limit by 1,024 and round down a little: 500 KB → 0.47, 300 KB → 0.28, 200 KB → 0.19, 100 KB → 0.09. Rounding down also covers portals that count a kilobyte as 1,000 bytes. The smallest target accepted is 0.05, about 50 KB.
Switch scans to grayscale
For scanned or photographed paper, tick Also convert to grayscale. Color is the largest part of a scan, and a page of black text on white paper loses nothing readable without it. On small targets this one checkbox often decides whether the file fits at all.
What is realistic
The compressor tries progressively stronger settings, down to images at 36 dpi, and stops as soon as the file fits. Under 200 KB, a few scanned pages in grayscale fit and stay legible; ten or more scanned pages usually can't without becoming hard to read. Text-based PDFs — exported from Word, Google Docs or a website — hold far more, because their text is stored as text rather than as a picture of it, and compression never rasterizes it.
When the target can't be reached, you still get the smallest version the tool could make rather than an error, so check the size before you upload and decide what to trim.
Trim before you squeeze
Every page you remove frees space for the pages that matter. Delete blank backs of double-sided scans and anything the form didn't ask for with Remove pages, then compress. If you are scanning from scratch, scan at 150 dpi in grayscale: a small file is much easier to make from a modest scan than from a 600 dpi color one.
If the portal accepts several uploads, split a long document and compress each part to the limit. Several readable files beat one that nobody can read.
Check before you submit
Open the result and zoom to 100% on the smallest print — stamps, signatures, ID numbers. A portal rarely rejects a slightly soft scan, but the person reviewing it will reject one they can't read.
Step by step
- Remove unneeded pages — Optionally drop blank or extra pages with Remove pages first.
- Choose Target size — In Compress PDF, switch to Target size and enter your limit in MB, rounded down: 0.19 for 200 KB, 0.47 for 500 KB.
- Tick Also convert to grayscale — Recommended for scans and photographed pages.
- Check the result — Confirm the size is under the limit and the smallest text is still readable, then download.