1 MB is the usual limit for email attachments on some portals, for court and tender filings and for multi-page application packs. Longer scanned documents fit with readable text.
Most can. The tool tries stronger settings until the file is 1 MB or less. If a long scanned PDF still will not fit, split it with Split PDF by size, or remove pages you do not need, and try again.
The tool first tries to shrink the file without any loss, then picks the highest quality that still fits your target. To reach small sizes, pages are saved as images, so the text stays readable but may no longer be selectable. Check the result before you upload it.
No. It is compressed inside your browser, so it never leaves your phone or computer.