Cold legs and feet are hugely uncomfortable, but wearing boots all day may not be practicable. There are lots of alternatives.
Good, long, socks designed for fishermen and outdoor sports may help, and of course can be worn all day.
Sheepskin slippers are naturally warm, and warm feet help the legs. You can buy some that are calf high.
You can buy heated socks - they are battery operated and do work:
http://www.lazyboneuk.com/store/pro579.html
If he needs rugged boots for outdoor wear, lined motorcycle boots may be ideal. These are meant to be warm.
If he prefers a softer, more casual style Uggs are sheepskin and are supposed to be excellent. I have never tried them but friends swear by them. There are a lot of fakes around, so be aware of that.
Many men who suffer in this way wear thick ladies tights under their trousers. Plus socks, naturally. :)
It sounds weird, but a lot of bus drivers, lorry drivers and fishermen swear it works! It is a cheap option to try, but is awkward in public lavatories.
Finally - I do hope your friend has discussed this problem with his GP. I could be a circulation problem that needs treating.