A project has seed file of 2D of default design model, default sheet model & DPF sheet model. How to convert all these 2D seed to 3D in MX Road SS4 V8i?
That depends on the configuration - from your earlier post, it looks like you used 'Bentley-Civil-Imperial' project, so it reads them from C:\ProgramData\Bentley\PowerInRoads V8i (SELECTseries 4)\WorkSpace\Projects\Examples\Bentley-Civil-Imperial\dgnlib\
This is a separate topic to seed files, and should be in a different thread.