How can I use standard built'in windows8.1's voice engines (speech engines) on my Windows 7? Should I install any SDKs or manually move some files (dll files, etc) to windows 7 and use them directly?
You can't. There's lots of implicit state that isn't encapsulated in DLL files.
(I'm assuming you're talking about TTS engines, not speech recognition engines. The SR engines haven't been updated from Windows 7 to Windows 8.1.)