What actually makes a PDF smaller
Most bulk comes from embedded photos and high-DPI scans, not from the words. Light trims object streams without flattening text. Balanced re-encodes page images at a readable ebook-style DPI. Maximum uses screen-style Ghostscript settings when a portal names a hard kilobyte cap. Uploads travel over HTTPS and are deleted after you download. Free covers everyday files up to 12 MB; Pro raises the cap and queues multi-file or oversized packs on dedicated workers.
Pick a preset before you guess
Start with Light on a native digital report — fonts stay sharp and the save is often enough for email. Use Balanced on camera scans so lab values and signatures stay legible. Jump to Maximum only when a job board or embassy names 100–500 KB. Over-crushing a scan until the type becomes mush is the usual failure; if the output is unreadable, go back one step instead of scanning the paper again.
What this tool is not
Compression is not OCR. It does not unlock a password file, merge several PDFs, or redact names. Unlock first if the document is encrypted. Split a 200-page scan if you only need three pages under a tiny cap. Merge after shrinking if you still want one packet.
Where to go next
Need a named kilobyte target? Open Compress PDF to a Specific Size. Sending through Gmail or WhatsApp? Use the email-and-sharing guide. On a phone, the mobile compressor uses the same three presets.