What PDF compression settings actually change

Compress PDF does not squeeze the file like a zipper. Ghostscript rebuilds it. Images are resampled, fonts may be subset again, and the internal structure is new. That is why a “smaller PDF” can also look softer, and why a tiny text-only file sometimes does not shrink at all.

Screen is the aggressive preset, the one PDF callers know as /screen. It is for a portal that measured the attachment and does not care about a stamp’s edges. Balanced uses the ebook preset. High uses the printer preset and often saves less. If the rebuilt file is not smaller, DocuLite downloads the original and tells you so. There is no fake percentage.

Compress a duplicate you are about to email. The working files on the server are deleted when you download them, and leftovers are removed within about 10 minutes. The bytes are not kept to study what the document said.

Encrypted files stop before Ghostscript runs. A password field is intentionally missing. If the document is damaged, the job fails with that reason instead of returning a partial file.