I have a very similar question to this question. I have only one version of python 3.5 installed on my Windows 7 64-bit system. I installed Anaconda3.4 via official website
If you are using Anaconda3 then you should already have numpy installed. There is no reason to use pip. My guess is that the Anaconda distribution is possibly not on your path and you are picking up some other system python.
You should run where python (or where python3) to see which one you are using. If the executable is not in the Anaconda install, then that is your problem and you will need to edit your path environment variable to ensure that you are opening the python you want.