The file is likely a Microsoft Project plan. Since it has the .mpp extension, it contains comprehensive data such as project tasks, timelines, resources, and budgets.
: You can import .mpp files into Planner to view them online, though some formatting or resources may be lost. Projekt_DO.mpp
💡 : If this is a work file you cannot open, using a free online viewer is the fastest way to access the data without a license. Microsoft Project / Planner question The file is likely a Microsoft Project plan