You cannot protect a folder directly, but the following
procedure makes doing it pretty easy.
Open the first document in the folder, password protect it, then step through the remaining documents one-at-a-time clicking the Key Icon and moving to the next document.
This will add password protection to each document.
Then, when you use it, once you enter the password for any document in the folder it remembers the password as you move from document to document until you quit or change to a document with