When ESRI products are used to create a GEO-PDF, if the file is created from a Layout, the Entire Map (with border graphics) contain a coordinate system and any data frames that are the actual mapping data are also assigned a coordinate system. When Opened as a Raster Reference, MicroStation reports that due to the multiple coordinate systems, the geo reference data will be ignored.
It would be much better if the software offered a list of the coordinate systems found and allowed the user to select one. In our case, our cartographic unit must create the map with borders, but for us to use their maps, we need them to create a separate, new product, adding to their workload. And as near as we can tell, the coordinate systems are all the same, as when we use Acrobat Viewer, we see the same lat long values across the entire map and only see measuring units change depending upon when we are within the border or are within the mapping limits.