how to simulate .bdf files in ModelSim-Altera

Your approach is the correct one. What you have probably done is create a HDL file for the top level. If you open this file in a text editor this will show you the interconnections between all of your blocks.

However you are also missing the HDL for the other components in your top level ie BUSMUX

You must also create a HDL file for the BUSMUX primitive. Just open the BUSMUX primitive in another BDF file and create a HDL file for this primitive.

Once this HDL file is created then you can add this file to the compilation list in modelsim.

This will make sure all files are needed for your design.

You would have probably got a binding error if you initially tried to start modelsim since the BUSMUX HDL file was missing from your original compilation

Thanks