Getting a PDF under 1 MB without ruining it
Hitting an exact size limit is a balancing act: too little compression and the upload is rejected, too much and the scan becomes unreadable. This page approaches 1 MB in steps and stops at the first quality level that fits, so you keep the best possible image for that size.
If your document is mostly text, expect a large reduction with no visible change at all. If it is a photographed page, expect softer detail — shooting the page in better light usually helps more than heavier compression.