Reviewing documents - Word, Excel, Powerpoint

Another question:

I'd like to use the custom properties to record who has created, checked and reviewed documents (this is available in word, PowerPoint and also Excel - go to file - properties, and then click on the custom tag in the dialogue box that comes up). Can someone explain the easy way to use this system as the MS Office help notes make no sense.

Is there anyway that the information recorded here can be automatically saved as a property when the file is pdf'd?

Once a file has been completed and signed off, is there a way, other than pdf'ing, of locking down the file so that it can no longer be edited? (I guess we can make it read-only at least - but is there any other cleverer way of doing this? I guess this comes under the heading of version control)

Thanks

Susan