The Choose Destination Document dialog provides controls to specify the target schematic document on which to move the currently selected design objects when using the refactoring feature. Refactoring allows circuitry to be moved around between the project's source schematics and is particularly useful where a sheet is becoming overloaded, or the circuitry is better contained as a sub-sheet that is referenced by a sheet symbol on a sheet above it in the hierarchy.
The dialog is accessed from the schematic editor by selecting the design objects constituting the circuitry to be moved then clicking Edit » Refactor » Move Selected Subcircuit to Different Sheet from the main menus.
The dialog lists all candidate schematic documents for the project that can legitimately be used as the target sheet for the move. Click on an entry to select the required document.