You run a PDF through compression, and the "after" size is almost the same as the "before." It feels like the tool failed, but usually the file simply has nothing heavy left to remove. Here is how to work out why, and what to try next.
Reason 1: The PDF Is Mostly Text
Text is stored as characters, not pixels. A 50-page report exported from Word might be 400 KB, and no preset can squeeze text much further. If your file is text-only and under 1 MB, it is already efficient.
Reason 2: Images Are Already Small
If the images inside were resized before the PDF was made, there is little resolution left to reduce. Compression will not go below the target resolution of each preset.
Reason 3: Vector Graphics and Charts
Maps, CAD drawings, complex charts and design files often contain thousands of vector shapes. These are not photos, so image compression does not touch them. Exporting the drawing as a flattened image can help, but you lose the ability to zoom infinitely.
Reason 4: Heavy Fonts
Some documents embed several complete fonts. Decorative fonts and large script fonts add weight that compression cannot remove. Re-exporting with a standard font, or with font subsetting enabled, is the fix.
Reason 5: Too Many Pages for the Limit
Sometimes the content is simply larger than the limit allows. A 60-page scan will not reach 500 KB and stay readable.
What to Do Next
- Try a stronger level. Compare screen, ebook and printer and go one step down.
- Remove unnecessary pages with Remove Pages, or keep only what is required with Extract Pages.
- Split the file into parts with Split PDF if the portal allows multiple uploads.
- Rescan smarter — lower DPI and greyscale make a huge difference, as explained in compressing scanned PDFs.
- Start from the original. Compressing a file that was already compressed gives poor results.
A Quick Decision Guide
| Situation | Best next step |
|---|---|
| Text-only, under 1 MB | Nothing — it is already small |
| Scan still large | Rescan in greyscale at 150 DPI, then compress |
| Too many pages | Remove or split pages |
| Drawings or charts | Export as image or accept the size |
When nothing else works, ask the recipient if you can send the file as a shared link or in several parts. Most offices will accept a sensible alternative.
How to Check What Is Inside Your PDF
You do not need special software to get a rough idea:
- Select text: if you can highlight words, the text is real and small.
- Zoom in on images: if photos stay sharp at 300–400%, they are high resolution and compressible.
- Count scanned pages: image-only pages are usually the heavy part.
- Compare size to page count: more than 1 MB per page almost always means large images or scans.
This quick check tells you whether to compress harder, rescan, remove pages or accept that the file is already as small as it sensibly can be.
Talk to the Recipient
If a document genuinely cannot meet a limit without becoming unreadable, a short message explaining this is often the fastest solution. Offer a split version or a shared link; most offices would rather have a readable document than a blurry one.
