Importing a Visual OTTHYMO v2.4 and higher project file (*.voprj) is necessary when you want to bring an existing scenario into your current project. This may be necessary if you are combining projects or if you want to use an existing model scenario to build a new model.
Once you have your project open, select File -> Import -> Import VH Scenario (Current Project) menu to browse the VO project file and open the Import Scenarios window as follows. All scenarios in the project are listed in the window. You may want to only select the scenarios that you want to import. Click Import Selected button at the bottom and the selected scenarios are added to current project.
Before running your new scenario, you should check that the storm files and any external files (e.g. READ HYD) are referenced to the proper location on your system.