Quick answer
Open Compress PDF and choose "Rasterize & recompress". Lower the render scale to about 1.0, then lower the JPEG quality a step at a time until the size fits. Remove pages the portal does not need before you start. Aim a little under the limit, for example 95 KB for a 100 KB limit.
Step by step
- Open Compress PDF and add your file.
- Try "Structure only" first. If the PDF was typed in Word or exported from a website, this may already be enough.
- If it is still too big, choose "Rasterize & recompress".
- Move the render scale slider down, for example from 1.5x to 1.0x, and compress again.
- Still too big? Lower the JPEG quality slider in small steps, for example from 0.70 to 0.55, and compress again.
- Zoom in on the smallest text in the result. When the size fits and the text is clear, download it.
Is 100 KB realistic for your file?
The limit is shared by every page. Divide the limit by the number of pages to see how much each page can weigh:
| Portal limit | 1 page | 3 pages | 5 pages | 10 pages |
|---|---|---|---|---|
| 100 KB | 100 KB per page | about 33 KB per page | 20 KB per page | 10 KB per page |
| 200 KB | 200 KB per page | about 66 KB per page | 40 KB per page | 20 KB per page |
| 500 KB | 500 KB per page | about 166 KB per page | 100 KB per page | 50 KB per page |
A page of typed text is usually light. A page that is a phone photo or a scan is much heavier. So a one-page certificate can often reach 100 KB, while a ten-page scanned document at 10 KB per page will usually look too rough to read. In that case, cut pages or ask whether the portal accepts several files.
The order that saves the most
- Remove pages first. Instruction pages, blank backs and duplicate copies cost space. Keep only what is asked for with Split PDF, then put the kept pages back together with Merge PDF if needed.
- Structure only. Lossless and quick. Text stays selectable.
- Rasterize at default settings. Check how far that gets you.
- Lower the render scale. This has the biggest effect on size. Text often stays readable at 1.0x and below.
- Lower the JPEG quality last. Stop one step before letters start to look blotchy.
Always compress again from the original file, not from a copy you already compressed. Each round on a compressed copy loses more detail.
If you are making the PDF from photos
When you photograph pages yourself, it is easier to shrink the photos first and build the PDF afterwards:
- Shrink each photo to its share of the limit with Compress Image to KB. For a 3-page PDF under 100 KB, try about 28 KB per photo to leave some room.
- Combine the photos with JPG to PDF.
- Check the final size. If it is slightly over, lower the KB target a little and rebuild.
Good photos compress better. Shoot in daylight, hold the phone straight above the page and avoid shadows.
What portals mean by 100 KB
Some portals count 1 KB as 1,000 bytes and others as 1,024 bytes. A file that your computer shows as 100 KB may be rejected. Stay a few KB under the limit, and check the size the way the portal shows it if you can.
Some forms also set a minimum size. If your file is under the minimum, compress again from the original with a higher JPEG quality.
On a phone
Compress PDF works in the browser on Android and iPhone. Pick the PDF from Files or Downloads, compress it, and the result is saved to your downloads. You do not need an app.
Good to know
No tool can promise an exact size, because the result depends on what is in your PDF. Rasterizing turns pages into images, so keep the original for your records. Your PDF is compressed on your device and is not uploaded, which is useful for ID documents and marksheets.
Frequently asked questions
Can every PDF be compressed to 100 KB?
No. It depends on how many pages the file has and what is on them. A one-page scan can usually get there with Rasterize and lower settings. A long scanned document often cannot without removing pages.
Which setting should I lower first?
Lower the render scale first, then the JPEG quality. Change one step at a time and check that the smallest print is still readable.
Will my text still be selectable?
With Structure only, yes. With Rasterize and recompress, every page becomes an image, so the text can no longer be selected or searched. Keep your original file.
Is my document uploaded when I compress it?
No. Compress PDF runs in your browser, so the PDF stays on your device. That matters for ID cards, marksheets and other personal documents.