2026-09-18
Text-only PDFs are usually a few hundred kilobytes. When a file weighs tens of megabytes, the culprit is almost always images — high-resolution scans embedded as bitmaps, uncompressed screenshots, or the same large picture referenced repeatedly.
Embedded full font families and leftover objects from past edits quietly add weight, too.
Lossless mode only restructures the file: it removes redundant objects, collapses duplicate references and reclaims unused resources. Zero quality loss — ideal for contracts, tenders and papers.
The benefit depends on how optimized the original already is; a well-optimized PDF may barely shrink.
Lossy mode re-encodes page images at a chosen quality: lower effective resolution, higher compression. A 300 DPI print-grade scan can drop to 150 DPI screen grade — visually indistinguishable on screen, but noticeable when zoomed or printed at high quality.
Email attachments and web sharing: "smart" or "strong" — a few hundred MB of scans can become a few MB. Printing or archiving: "light" (lossless) to preserve every detail.
Keep the original, then compare key pages (signatures, stamps, small tables) at high zoom before committing to the compressed copy.
If nothing reduces the file, it is most likely a text/vector document — already efficiently encoded. "Not compressible" is normal, not a defect; there is no need to keep trying.