The three that cause the trouble
Tracked changes carrying internal negotiating positions. Redactions applied as a shape over text rather than a removal of it. Document properties naming a colleague, a client or a matter number that the other side was not meant to have.
A working sequence
Finish the document. Accept or reject every tracked change. Delete all comments. Remove content properly rather than covering it. Export a fresh PDF rather than sending a working copy. Confirm the author field is empty. Then attach it.
Received files deserve the same attention
The check runs both ways. A document that arrives from the other side may carry its own tracked changes and properties. Reading them may be improper depending on your jurisdiction and rules of professional conduct — but knowing they are present is the first step to handling them correctly.
Why in-browser matters here
Privileged material should not be uploaded to a third-party service for processing, whatever its retention policy says. This page never transmits the file. You can verify that in the browser's network tab before you trust it with anything.