How to Compress a PDF Without Losing Quality
To compress a PDF without visibly losing quality, use the High quality preset rather than a size target — this compresses the document's container structure and re-encodes images conservatively, preserving detail while still reducing file size. True "zero quality loss with maximum size reduction" is not physically possible when a PDF contains raster images, since image compression is inherently a size/quality tradeoff.
What actually shrinks a PDF's size
Most size reduction comes from re-encoding and downsampling embedded raster images (photos, scanned pages) and cleaning up the document's internal structure. A PDF that's mostly text and vector graphics has little to compress — it's already small relative to a scanned equivalent.
Choosing the right preset
High quality keeps the most visual detail with modest size reduction — best for documents where photos matter (portfolios, print-ready files). Balanced is a good default for most everyday documents. Strong maximizes size reduction and is best reserved for cases where hitting a small size matters more than pixel-perfect images, like email attachments.