How to reduce PDF file size
Open Compress PDF, choose Balanced, press Start and check the new size. If it's still too big, use Strong or type a target size in MB.
If it barely shrinks
Your file is probably mostly text and fonts. Try Delete PDF pages, or split the file into parts.
Scans and photos
These shrink the most. Strong can cut a phone-photo PDF by over 90%, though images look softer when zoomed in.