What Makes a PDF File Large in the First Place?
PDF files balloon in size for a handful of reasons, and knowing which one applies to yours helps you get the best compression result. The biggest culprit is almost always embedded images — a PDF with pages of high-resolution photos or scanned pages is essentially a collection of large image files wrapped in a container. A single 300 DPI full-page scan can weigh 2–5MB on its own. Multiply that by 50 pages and you understand why scanned documents are often enormous. The second factor is embedded fonts: a PDF often bundles the entire font file so the document looks the same on every device, even if only a fraction of the font's characters are actually used. Object overhead, duplicate resources, and metadata also contribute, though typically to a lesser degree than images and fonts. Our compressor addresses all of these simultaneously when you click compress.