uses Windows;
procedure ShowDllPath stdcall;
var
 TheFileName: array[0..MAX_PATH] of char;
begin
 FillChar(TheFileName, sizeof(TheFileName), #0);
 GetModuleFileName(hInstance, TheFileName, sizeof(TheFileName));
 MessageBox(0, TheFileName, 'The DLL file name is:', mb_ok);
end;

function GetModuleFileNameStr(Instance: THandle): string;
var
 buffer: array [0..MAX_PATH] of Char;
begin
 GetModuleFileName( Instance, buffer, MAX_PATH);
 Result := buffer;
end;
GetModuleFileNameStr(Hinstance); // dll name
GetModuleFileNameStr(0); // exe name