How do I install the Avogadro-Packmol-Extension-master plug-in in the windows version of Avogadro
If you’re talking about Avogadro 1.2, the short answer is that you can’t. In that version, you have to compile the packmol extension against Avo1.2 on a particular platform (Windows in your case). At this point, that’s not possible since the older compiler and Qt4 used in Avogadro 1.2 are not supported.
There’s some work for Avo2 to have a Packmol extension, but it’s not yet released. In that case, it’ll be a Python script, so it can run on any platform with a Python environment.