How to get text from Adobe Reade window like MS Word

I know can text from MS Word window like this:
CLSID clsid;
CLSIDFromProgID(L"Word.Application", &clsid);
IUnknown *pUnk = NULL;
HRESULT hr = GetActiveObject(clsid, NULL, (IUnknown**)&pUnk);
then via pUnk interface can get text from the Current instance MS Word.

then how can I get text from an Adrob Reader window.