Proteus - How to manually load the schematic's components in the PCB view?
I haven't used Proteus, but in other ECAD packages, you have to define PCB footprints in the schematic symbols.  Then the footprints will be listed in the netlist passed to the PCB program.

Usually, you would define a default footprint when you create the schematic symbol, but you should also be able to set the footprint after placing the component on the schematic.