The Document object has several properties related to document passwords:
This read-only property returns True if a password is required to open the specified document.
Sets a password (as a string) that must be supplied to open the document. This an example of a relatively rare write-only property. In other words, you can write the password, but not read it!
Sets a password for modifying the document (that is, writing to the document, hence the name). It is also a write-only string. Note that a document can still be opened without knowing this password.