What you can change
The title, author, subject, keywords, the application that created the document and the software that wrote the PDF. The current values are filled in for you; edit what you want and save.
Removing information before you share
Leave a field empty and it is removed from the file outright, not stored as a blank. That is the quick way to strip an author name or an internal project title from a document you are about to send.
What this does not touch
Only the document-information fields. Text inside the pages, comments and annotations are left as they are, and so is any separate XMP metadata packet the file may carry. Creation and modification dates are not editable here.