PDF Compression: What Shrinks and What Does Not
The size is in the images
A page of text is tiny — often a few kilobytes. A single high-resolution photo can be several megabytes. When a PDF is much bigger than the page count suggests, it is almost always the images.
Why some PDFs barely change
A text-only PDF — a contract, an essay, an invoice — is usually already small. Do not expect a large reduction on something that started at a few hundred kilobytes. The big wins come from documents with photos, scans, or complex graphics.
Picking the right quality level
High quality (80–95%) is a safe default for anything with photos people will look at closely. Lower settings (40–60%) are for internal drafts and files that just need to be small. Start high and work down if you need more compression.
If you only need to get under a 25MB email limit, start with 70% quality. You will usually clear the limit with less quality loss than you would expect.