GH_InputParamManager AddFilePath howto

I am new to grasshopper development. I am trying to create a new GH node to read and convert and an external data file.
I am using VC2017 Community edition.
Currently I am using GH_InputParamManager.AddTextParameter to register the input as text.
How to proceed, if I have to get the input parameter directly as a path to the file? Similar to Import3DM, ImportImage components in Grasshopper… I could not find a AddFilePathParameter method…