Pdf to Microstation conversion software

I'm not all that familiar with MicroStation, but isn't it 3D? There shouldn't be any software to handle that transition.

If you just want to make a 2D drawing, IF the PDF is vector based, you may be able to open it up in a program like Rhino and export an IGES or other format importable to MicroStation. However, your mileage will definitely vary. PDFs can contain raster images which Rhino wouldn't be able to convert, and even in vector based PDFs, the curves may be made of line segments or otherwise composed of oddly shaped curves.

A better route would be to get a 2D DXF or DWG of the CAD model. But you wouldn't be asking if you had that option, I gather.

Best of luck, this may be a very hard task.