Usually because the PDF is made of scanned images, has many pages, or the limit is too small to keep every page readable. A compressor can only remove detail; when a 20-page scan must fit in 200 KB, each page gets about 10 KB. Split the PDF, scan in grayscale at a lower resolution, or use a compressor built for scans.

The common causes

  • Scanned pages are photos. A phone or scanner saves each page as an image. Text PDFs made from Word are tiny; scans of the same page are many times larger.
  • Colour and high resolution. Scanning a marksheet at 600 DPI in colour stores far more detail than a portal needs. Grayscale at 150–200 DPI is usually still sharp.
  • Too many pages for the limit. Divide the limit by the page count. At a few KB per page, text starts to blur.
  • Already compressed. If the PDF was compressed before, there is less left to remove; a second pass gains little and costs quality.
  • Embedded fonts and graphics from design tools such as Canva. These keep the PDF large even with few pages.

What to do

  1. Check the page count. If the portal wants one document, upload only the pages it asks for: split the PDF first.
  2. Use the scan-tuned compressor. The scanned document compressor keeps text contrast while reducing image detail.
  3. Rescan smarter if you still have the paper: grayscale, 150–200 DPI, cropped to the page.
  4. Type the exact limit instead of picking a level: compress PDF to a KB size. CompressKaro tells you if the result is still over the limit.