1. Start with Balanced
Open Compress PDF and keep Balanced. It shrinks photos and keeps text sharp. If the file is still too big, try Smallest.
2. Scans behave differently
A scanned page is a picture. Compress tries two methods and keeps the smaller file. If pages are re-rendered as images, text can no longer be selected, and the result tells you which happened.
3. Still too big? Send it in parts
Use Split PDF to cut it into two or more files, then tell the reader the order.
Good to know
Attachment limits vary by provider. If a file is still big after compressing, check for large photos: converting a colour scan to greyscale can also help.
Questions
Will compressing lower the quality?
Images may lose some detail at stronger settings. Text stays sharp. Start with Balanced and compare.
Can I compress on my phone?
Yes. It runs in the browser on phones too; very large files are safest on a computer.
Related: Split a long PDF into parts · Why on-device tools are safer