A job portal that rejects your application because the PDF is a few KB over its 200 KB limit is a miserable way to spend an evening. Most advice says “use a PDF compressor” and leaves out the part that decides whether it works: what kind of PDF you have. We ran three different PDFs through our own Compress PDF tools, at every setting, and recorded what came out. Two of the results are the opposite of what you would expect.
What our compressor actually does
Before the numbers, it matters how the tool works, because it is a trade-off, not magic. The Compress PDF tool draws each page onto a canvas at a chosen resolution (DPI), saves it as a JPEG at a chosen quality, and builds a new PDF from those pictures. That is why it works well on scans and badly on text. The three presets are:
| Preset | Resolution | JPEG quality |
|---|---|---|
| High compression | 100 DPI | 55% |
| Balanced (recommended) | 150 DPI | 72% |
| Best quality | 200 DPI | 85% |
It runs in your browser, so the file is not uploaded. The cost of that approach is that text in the result is part of the picture: you can no longer select, copy or search it.
What happened to three different PDFs
We tested a one-page text report (the sample PDF our tools ship with), a five-page PDF built from screenshots of our own tool pages, and a three-page PDF built from our two sample photos. Each went through all three presets.
| Test file | Original | High compression | Balanced | Best quality |
|---|---|---|---|---|
| Text report, 1 page | 2.1 KB | 56 KB (+2,559%) | 108 KB (+5,060%) | 199 KB (+9,408%) |
| Screenshots, 5 pages | 1,412 KB | 229 KB (−84%) | 534 KB (−62%) | 1,015 KB (−28%) |
| Photos, 3 pages | 571 KB | 94 KB (−84%) | 221 KB (−61%) | 597 KB (+4%) |
Two things stand out. First, the text report grew by 26 to 94 times its original size. Second, the photo PDF was already efficient, so the Best quality preset made it slightly larger. The tool tells you when this happens (“This PDF is already small or text-based, so re-rendering pages made it larger”) and you should believe it.
Getting under an exact limit
Portals ask for 1 MB, 200 KB or 100 KB. The size-limit versions of the tool try a ladder of settings, from 150 DPI at 72% quality down to 50 DPI at 25%, and keep the sharpest one that fits. This is what they chose for our two image PDFs:
Both files fit every limit, but at very different cost to sharpness. The photos only needed 130 DPI for 200 KB because the pictures inside were small to begin with. The screenshots needed 84 DPI, and 60 DPI for 100 KB, because they carry a lot of fine detail. If your document is mostly small print, the lower limits are where it stops being readable.
What a DPI number means for readable text
A point is 1/72 of an inch, so text of a given size is that many points times DPI ÷ 72 pixels tall. For 11-point body text:
| DPI | Height of 11-point text |
|---|---|
| 200 | 31 px |
| 150 | 23 px |
| 100 | 15 px |
| 84 | 13 px |
| 60 | 9 px |
| 50 | 8 px |
This is arithmetic, not a legibility test, but it explains the problem: at 60 DPI the text is under 10 pixels tall, which is hard to read on a printout and worse when the reviewer zooms in. After compressing, always open the result and read the smallest text on the page before you upload it.
When the result is too blurry
You have three better options than accepting an unreadable file.
- Send fewer pages. Size scales with page count. Use Split PDF or Extract Pages to keep only what the portal asks for, then compress that.
- Shrink the pictures before they go into the PDF. If you build the PDF from photos or scans, resize and compress each image first, then use JPG to PDF. We built our three-page photo PDF four ways:
| Pictures put into the PDF | PDF size |
|---|---|
| 1024 px wide, JPEG 92% | 571 KB |
| 800 px wide, JPEG 80% | 214 KB |
| 640 px wide, JPEG 75% | 129 KB |
| 500 px wide, JPEG 75% | 87 KB |
Choosing the width yourself lets you decide where to give up detail. Our image compression guide shows how size responds to quality and dimensions.
- Keep text as text. If the file is a document you wrote, re-export it from the program that made it rather than compressing a finished PDF. That keeps the text sharp and searchable.
Step by step
- Check whether you can select text in the PDF. If you can, try re-exporting it before using a compressor.
- Open Compress PDF, choose the 200 KB limit (or 100 KB or 1 MB) and add your file.
- Wait for the result, which shows the final size and the DPI it settled on.
- Download the result and open it. Read the smallest text on every page.
- If it is too blurry or still too large, use one of the options above and try again.
The tools work in your browser and nothing is uploaded. These results come from three files we built or already had; your document will differ, and a scan with fine print or a very high page count can need other trade-offs. We did not test password-protected PDFs, or compare against other desktop programs.
