Compress PDF to 200 KB.

200 KB sits between the aggressive 100 KB limit and the more forgiving 300–500 KB range. For a single-page scanned certificate, 200 KB provides a good balance: text is clearly legible, seals are recognisable with reasonable detail, and photographs retain enough clarity for identification.

This is a common limit on state government portals, scholarship applications, and some competitive exam registration forms where the portal designers chose a tighter constraint than the 300–500 KB range but recognised that 100 KB was too aggressive for document verification.

Here's what actually changes across these three common size targets for a typical single-page colour certificate scan (original: ~3.5 MB at 300 DPI):

At 100 KB (2.8% of original): Text is readable but may show softening on fine print. Seals lose edge detail. Photographs show visible compression artifacts. Light watermarks may disappear.

At 200 KB (5.7% of original): Text is clearly legible including fine print. Seals retain most detail — perimeter micro-text may still be soft. Photographs are identifiable with moderate softening. Watermarks are faint but visible.

At 500 KB (14.3% of original): Near-original quality for text and seals. Photographs retain good detail. Watermarks and fine decorative elements are preserved. Most viewers wouldn't notice the compression.

The jump from 100 KB to 200 KB is the single biggest quality improvement per kilobyte — if your portal accepts 200 KB, always prefer it over 100 KB.

Use 200 KB when your portal specifies it, or when you need a margin below a 250 KB limit. If your portal says '200 KB or less', target 180–190 KB to account for potential binary/decimal KB measurement differences.

If your portal accepts 300 KB or higher, there's no benefit to compressing further. Use the larger allowance for better quality. Only compress to 200 KB when the portal actually requires it.