PDF compression reduces file size by re-encoding the images and streams inside a PDF. Understanding how it works helps you choose the right settings for your specific use case — maximum quality, minimum size, or somewhere in between.
PDF file size is dominated by embedded images. A single high-resolution photo scanned at 600 DPI can be 5–15 MB on its own. Text, vector graphics, and PDF structure are comparatively tiny. A 20-page PDF that is 50 MB is almost certainly full of uncompressed or losslessly-compressed page images.
PDF compression re-encodes embedded JPEG and raw pixel images at a lower quality setting and optionally resizes them to a lower maximum dimension. For example, reducing from 600 DPI to 150 DPI reduces pixel count by 16×, and re-encoding at 65% JPEG quality removes further redundant data — together achieving 80–90% size reduction without visible quality loss at screen viewing distances.
Basic (High Quality): JPEG quality 82%, max dimension 2400px — minimal visible change, 10–30% size reduction. Good (Balanced): JPEG quality 65%, max dimension 1800px — noticeable reduction, 30–60% smaller, recommended for email and web. Strong (Smallest): JPEG quality 42%, max dimension 1200px — maximum compression, 50–80% smaller, suitable for screen reading only.
Tip: For documents you will print, use Basic or Good. For documents viewed only on screens or shared via messaging apps, Strong compression is fine — text remains sharp at any compression level.
Compression does not reduce text size meaningfully — text is already compact. Compression does not help PDFs that are large because of many embedded fonts — use the Repair tool to strip unnecessary font data. And compression cannot shrink PDFs that are large due to hundreds of vector graphics or complex PDF structures.
Go to pdfeditor.onl/compress-pdf to reduce your PDF size. Upload, choose a profile, and download. The tool shows the original and compressed size so you can see exactly how much was saved.
No. PDF text is stored as vector outlines, not images. Compression only affects raster image data — text always remains sharp at any compression level.
Yes. At very low JPEG quality (below 40%), image artifacts become visible — especially on photos with smooth gradients. The Strong profile at 42% quality is near the practical lower limit for readable documents.
If the original PDF has no images (it is pure text or vector graphics), there is nothing for JPEG compression to act on. The tool can only compress what is there.