Well in the organisation I work for a controlled document is a document that is basically fixed. When you develop a procedure for instance it may be a quality management document concerning a purchasing procedure, once the procedure of how to select a supplier is set, then you lock that document and it's procedures into a controlled document.
In other words in my organisation people can see the document, but can't change it, only upper managemnet can change it. I did them for my company regarding engineering practices, method statement, risk assements, hazard logs etc, only the technical director and myself can change them, though the guys on site see them.