The File > Open command activates the Project Window and sets the focus on the text box of the Project Win­dow. If the Project Window was not visible, it is made visible, and then hidden after you select a file to open.

You can customize what the Open command does in the Options > Preferences: Files dialog box. Instead of activating the Project Window, you could have it bring up other dialog boxes or windows instead.

If you do not have a project open, then this command will bring up the system Open dialog box, which is a standard system dialog box.

You can also open a file by dragging a file and dropping it onto the Source Insight application window.