Your files stay yours. They are stored in your own account, or in a workspace you share, and are seen only by you and the people in that workspace.
They are not added to our reference material. Pages are classified by comparing them with reference documents we maintain; your files are compared with it and never join it.
Nothing is redacted unless you ask. Checking names, numbers and dates across documents is the review, so they are kept as they are. Redaction is a tool you run when you need a redacted copy.