Open Make PDF smaller from the Home screen (or use its own page link).
Tap Choose file and select your PDF from the phone or computer.
Need an exact limit? Tap My own size, then type the maximum size in KB (for 100 KB type 100; for 1 MB type 1024).
Tap the big purple Start button and wait a few seconds.
Check the result line, it shows the old and new size (for example 4 KB → 3 KB). If the text looks blurry, go back and choose a bigger size.
When you see Done!, tap Download. The new file is saved on your phone or computer.