Soft Drag is a tool preset that consists of the Move tool combined with Screen falloff. With this preset, you can select vertices, edges, or polygons and then drag them to affect their neighbors to a greater or lesser degree based on the Screen falloff. You use the right-mouse button to define the Screen falloff's circle.
You access Soft Drag from the Deform tab of the Modo Tools toolbar or by choosing Edit > Deform > Soft Drag.
Enable Transparent in the Screen Falloff section for the Soft Drag selection to happen through the mesh. With Transparent disabled, this tool preset only affects geometry facing the view.