Using the utility plugin "PSOFT Pencil+ 3 Converter", Pencil+ 2 data can be converted to Pencil+ 3.
PSOFT Pencil+ 3 Converter is a utility plugin used to convert Pencil+ 2 materials / standard materials to Pencil+ 3 materials, or to convert Pencil+ 2 lines to Pencil+ 3 lines.
Download the utility plugin here.