There is only one file type that uses the .OPJU extension:
Origin Unicode Project
An OPJU file is a project created by Origin 2018 and later, a data analysis and graphing application used by various scientists and engineers. It contains all child windows in the project, which may include worksheets, 2D/3D graphs, and matrices. OPJU files also store project variables, imported filters, results log contents, and metadata.
Updated: December 10, 2017