Are you using PDF for Portable Document Format?, the only instance I can think of where entering a certain 'zone' triggers an action is an App. on a smart phone called 'Where-I-Go', this is an offshute of Geocashing, you program what the player of the App. will do when a certain location is reached
To get a map contained in a PDF file onto a Garmin unit you would have to convert the PDF into a JPEG file, when you have a JPEG map it is possible to create a KMZ file that can be loaded onto some Garmin units and used as any other map, please not not all Garmin units can work with this type of map, there is a link (Click HERE) that explains the steps in making a KMZ file from a JPEG file and also has a list of Garmin units that can use this type of map