Use the Windows API function GetKeyState() to determine if a key is pressed in the main project source. To get to the main project's source file, select from the IDE's main menu, select "View">>"ProjectSource". Example:

program Project ;
uses
  Windows,
  Forms,
  Unit  in 'Unit .pas' {Form };
{$R *.RES}
begin
  if GetKeyState(vk_F8) <   then
   MessageBox(0, 'F8 was pressed during startup', 'MyApp', mb_ok);
  Application.Initialize;
  Application.CreateForm(TForm , Form );
  Application.Run;
end.