Delete the images from a PDF and keep the text. Because images are usually almost all of a document's weight, this can shrink a file far more than compression ever will. It is also a straightforward way to produce a text-only version of a document for reading or archiving where the pictures add nothing.
A scan is entirely images, so you would be left with blank pages - or with just the OCR text layer if the file has been through OCR. Compress PDF is what you want for a scan.
Text stays exactly where it was. The images simply disappear, leaving gaps where they used to sit, since nothing reflows.
No, this clears them all. To take out a single picture, redact the area instead.
Files are uploaded over an encrypted connection and processed on CoonTool's own server, not in your browser. The working copy is deleted automatically once the job is done, and in any case within 24 hours. Nothing is stored permanently and no account is required.