Why are PDFs so large?
The usual culprit is high-resolution images inside the file, especially in documents scanned with a phone or scanner. Embedded fonts and metadata add less, but they count too.
Method one: light compression
Open Compress PDF and choose the Light level. It optimizes the file structure and strips metadata without touching the pages, so text stays selectable and searchable. It suits text-based files, but its effect is limited on image-heavy ones.
Method two: strong compression for scans
If your file is scanned images, choose Strong: pages become compressed images, which shrinks the size a lot. The trade-off is that text is no longer selectable, so keep a copy of the original.
Extra tips
Merge several files first with Merge PDF and compress the result once. If printing is the goal, try PDF to Grayscale to save ink. And if a file is already optimized, the tool will have nothing to shrink and returns it unchanged.