If several exchange files are open in the program, then one of them is considered active at the moment.
Many operations are performed on the active exchange file, such as reparsing, sorting parcels/adjacencies. Also in the information panel, all information is given for the active exchange file - a list of objects, a list of points, information on selected objects.
If the Drawing tab is selected, you can choose the active exchange file from the information panel. If the bookmark of one of the open exchange files is selected, this file is the active one.
Also, the change of the active file can occur when you select a site on the map - if the checkbox "Search by point - search in all open files" is checked in the map settings