Open Workbench from the Start menu (well, it was start, it’s the Windows symbol thing, bottom left of the screen). Once WB loads File>Open and navigate to the desktop for the wbpj file.
I’ve seen a lot of people double clicking on files because of the “normal” Windows behaviour; with engineering/less common formats that can fail. For example, we use pdf files in Fluent that are Probability Density Function, and nothing to do with the document format! Fluent's pdf files may predate the document reader too.
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