A 40 MB PDF that will not attach to an email is a common, frustrating problem. The temptation is to crush it down hard — but aggressive compression turns crisp text into a blurry mess. Here is how to shrink a PDF sensibly.
Where PDF size actually comes from
Most of the weight in a PDF is images, not text. Vector text is tiny; full-page scans and embedded photos are huge. So the lever that matters most is how images are stored.
- High-resolution images embedded at full quality
- Duplicate or unused fonts
- Scanned pages stored as uncompressed images
- Embedded video or attachments
Compress without wrecking text
The goal is to reduce image resolution and quality just enough — usually to around 150 DPI for screen viewing, or 100 DPI for a quick preview — while leaving vector text untouched so it stays sharp and selectable.
- Choose a compression level matched to how the file will be used.
- Re-sample images rather than rasterising the whole page.
- Keep text as vectors — never flatten the page to an image.
- Check the result reads clearly before sending.
If you can still select and copy the text after compression, you have done it right.
Try it with SELKATDocs
SELKATDocs compresses PDFs in your browser with adjustable quality levels, so you can balance size against readability yourself.
Try the SELKATDocs Compress PDF tool →
A well-compressed PDF should be dramatically smaller — and still perfectly readable.