Remove the active and hidden parts of a PDF: embedded JavaScript, attached files, launch actions, external links and metadata. PDF is a far more capable format than most people expect - it can run scripts and carry arbitrary files - and those capabilities are both a malware vector and a way for information to leave your organisation without anyone noticing. Sanitising strips them while leaving the visible document intact.
Legitimately, for form validation and calculated fields. It is also a long-standing malware vector, which is why stripping it is a sensible default for documents arriving from outside.
The visible page content is left alone. What breaks is behaviour - interactive forms that relied on scripts to calculate or validate will stop doing so.
No. Sanitising targets active content and metadata, not page content hidden underneath a drawn box. Use Redact for that.
No. Flattening converts interactive elements into fixed page content so they still appear. Sanitising deletes active content outright.
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.