Guide
Why did PDF compression save so little space?
Compression depends on what the PDF contains. Photo-heavy scans can shrink substantially, while a text-only or already optimized PDF may change very little. Strong raster compression can also remove selectable text.
Compress PDF
PDF is a container, not one image format
A PDF can contain selectable text, embedded fonts, vector drawings, photographs, scanned page images, forms and attachments. Two files with the same page count can therefore have completely different sizes and compression potential.
Scanned color pages and high-resolution photos usually dominate file size. A mostly textual PDF may already be compact, so a second compression pass can produce little improvement.
Why common files barely shrink
- The source application already downsampled and compressed all images.
- The document is mostly text or vector graphics rather than large images.
- The PDF contains fonts, forms or attachments that image-quality settings do not reduce.
- The requested quality is intentionally high, leaving little room for further reduction.
- Encrypted or unusual PDFs can limit what a browser tool can rewrite safely.
What JustFileKit compression changes
The current compressor renders each page at roughly 120 DPI, encodes the rendered page as JPEG and builds a new PDF from those page images. This is effective for many scans because it reduces image resolution and encoding quality together.
The tradeoff is important: text and vector artwork become pixels. Text may no longer be selectable or searchable, form controls can be flattened, and fine lines may soften. Use the original file when those properties matter.
This method is best treated as a smaller sharing copy, not as a replacement for an archival, accessible or signed original.
Choose the right alternative
| Situation | Better action |
|---|---|
| Only a few pages are needed | Split the PDF and send only those pages |
| Pages are unnecessary color scans | Convert to grayscale before or during rescanning |
| Source document is available | Export again with optimized image settings |
| Selectable text must remain | Use a structure-preserving desktop optimizer |
| File is still too large | Reduce scan resolution or divide the document |
Check more than the final megabytes
After compression, zoom into small text, charts and signatures. Test copy-and-paste if selectable text matters, and verify links or forms if the document used them. A smaller number is not a successful result when it damages the information the recipient needs.
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