How to start a QT programm without copying the dll files

Question

I wrote a little Qt program (on Windows) and I met the following situation:

With CMake, I generated my make files to build the Program as follows

cmake_minimum_required(VERSION 3.5)
project(helloworld)

SET(C++_STD_FLAG "c++11" CACHE STRING "e.g. c++98,c++11,c++14,...")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=${C++_STD_FLAG}")

set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)
find_package(Qt5Widgets)

add_executable(main main.cxx)
target_link_libraries(main Qt5::Widgets Qt5::Gui Qt5::Core)

If I want to start the "main.exe", it appears a message that some DLL's are not found. The DLL's are Qt5Widget.dll, Qt5Core.dll, Qt5Gui.dll. If I copy them to the same folder as the "main.exe" everything work fine.

How can I launch the "main.exe" without copying the DLL's into the directory?

EDIT: The path, where the DLL is, is already added to the PATH variable in windows. However, it does not work.

EDIT: I also append my code of the main.cpp

#include <QtWidgets>
#include <QApplication>

int main(int argc,char **argv){
  QApplication app(argc,argv);
  QWidget window;
  window.setWindowTitle("Hallo Qt");
  QPushButton *button = new QPushButton("Ende");
  QVBoxLayout *layout = new QVBoxLayout;
  layout->addWidget(button);
  window.setLayout(layout);
  window.show();
  return app.exec();
}

EDIT: I found the problem, but this raise a furhter question: I also have installed PyQt, which had a higher priority in the PATH variable. So I made the other Qt installation a higher and it worked.

But, How can I tell an executable file to use a specific DLL? Because, if I compile the program with Qt Creater it works even if the PyQt has a higher priority in the PATH variable.

Thanks in advance