The EPW is a weather file format used to run simulations in EnergyPlus. EPWs are text files and can be opened and edited in any text editor, spreadsheet tools or open-source software tools for creating and editing customised weather files, such as the Element software developed by Big Ladder Software (https://bigladdersoftware.com/projects/elements/).
The EnergyPlus Auxiliary Programmes document (attached) describes EPW weather data and provides general information on weather data for energy simulations and weather file conversion.