hi tuna lover
sorry to say it can be a slow and painful process
the IDF file will create surface data/protrusion for all components based on the PCB design BOM
I usually import the data, turn it into a solid part then export as iges or step to try and reduce file size before placing in the assembly.
This reduces processing time, and allow for quicker clash detect analysis.
Furthermore the data that is exported from the PCB program is based on MAX envelope sizes for each component. Sometimes it is worth modelling critically placed or larger components to allow more/less space within the package design.
This is not ideal as every time the PCB up revs then you have to replace in teh assembly, so its not parametric.
Therefore you cant really attacehd copy geoms/publish geoms to the PCB data.
Like I say it can be a frustrating process depending on the amount of iterations you have to go through.
But to ensure the design works it sure beats the hell out of giving 2d sections to the PCB department to work to......