Can a free proton normally be changed to a free neutron by electron capture?
No, a free proton cannot normally be changed to a free neutron by electron capture.
The proton and neutron must be part of a larger nucleus.
During electron capture, the nucleus captures one of the inner electrons, usually from the K or L shell.
The capture converts a proton into a neutron and emits an electron neutrino. The net process is
But it has to happen inside a nucleus. For example,
You can see this happen iin the image below.