Thank you guys, for your interest in this matter.
My idea is more about a macro that runs automatically on the event of opening a SW file (not dependent of a hot key, or mouse click). The macro controls the content of some custom properties. If these properties have some values, then messeges are printed on screen. Otherwyse, the macro ends/pauses silently for the user.
Example: a part file as a custom property named "revision_in_study" with the value "yes". If some user opens this file (for use in an assembly, for example), the macro test the contents of the property and warns the user that this file will probably change (depending on the result of the study). I don't want the macro execution to be user dependent, for safety purposes.
I think that the bigest problem is not read the property. That can be solved based on the example that Bradley is showing. The bigest problem is having the macro on stand-by, wayting for a file to be opened, run after the file opens, and be on stand-by again.