If you have a bitmap in a raster project in Didger 3, you cannot import any additional files into the raster project.
If you are using Didger 3, you can overlay a vector or data file on top of a bitmap by exporting the calibrated bitmap from the raster project as a GeoTIFF. Then import this GeoTIFF into a vector project. Once the bitmap is imported into the vector project, you can overlay vector and data files on top of it.
Didger 4 and Didger 5 solve this problem as there is only one project type.
Updated March 20, 2014