"regsvr32.exe d3drm.dll" returns an error saying DllRegisterServer was not found.
I compiled the test below and ran it on an XP VM (which had the dx7 SDK installed) just to be sure that my native win8.1 box wasn't the issue:
CoInitialize(NULL);
hr = CoCreateInstance(&CLSID_CDirect3DRM, NULL, CLSCTX_INPROC_HANDLER, &IID_IDirect3DRM, &d3drm);
ok(hr == D3DRM_OK, "Got %#x for IID_IDirect3DRM\n", hr);
hr = CoCreateInstance(&CLSID_CDirect3DRMTexture, NULL, CLSCTX_INPROC_HANDLER, &IID_IDirect3DRMTexture3, &texture3);
ok(hr == D3DRM_OK, "Got %#x for IID_IDirect3DRMTexture3\n", hr);