What actually gets smaller
A document rewrite drops objects nothing on the page still uses. A scan that is already a tight JPEG often barely moves. A export full of unused fonts and images can drop a lot.
What this is not
There is no OCR and no 'make it 200 KB' control. If you need the pages as pictures, open PDF to JPG after this.
Limits
Free uploads are up to 20 MB. The result stays available about 30 minutes, then it expires. We do not keep a library of your files.