A 40-page PDF that's mostly text should be a few hundred kilobytes. If yours is 40 megabytes instead, it's almost never the text causing that — it's the images.
What's actually making your PDF huge
- Scanned pages saved as high-resolution images — a single scanned page at 600 DPI can be several megabytes on its own
- Embedded photos or graphics saved at print resolution when the document is only ever viewed on screen
- Fonts embedded multiple times across different pages instead of once
Text itself is almost never the problem — it's tiny. Compression tools work by targeting the images specifically.
What "compression" actually does
PDF compressors typically do two things: re-encode images at a lower resolution or quality setting (similar to how a JPEG can be saved at different quality levels), and remove redundant embedded data like duplicate fonts.
This is why compression can reduce file size dramatically without the text looking any different — the text was never the large part to begin with.
Where quality loss actually shows up
If a PDF looks blurry after compressing, it's almost always because the images were compressed too aggressively for their intended use. A photo destined for print needs higher quality than one that'll only ever be viewed on a screen.
A quick way to tell if compression will actually help
- If your PDF is mostly text (a contract, a report, an article) — it's probably already small, and compression won't do much.
- If it's mostly scanned pages or embedded photos — compression can often cut the size by 50-90% with minimal visible difference for on-screen viewing.
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See Itqan PDF →The honest bottom line
Compression trades some image quality for file size, and how noticeable that trade-off is depends entirely on what's actually in your document. For text-heavy files it barely matters; for scan-heavy or photo-heavy files it can make a real difference in both directions, so it's worth checking the result before sending it somewhere quality actually matters.
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