Once you have downloaded 2 files:
1. Companies that you want contacts for
2. All Contacts(or I generally use filter of country, other customized field to avoid downlaoding huge chunk of it)(Tip: Make sure you download contacts where “Associated Company” is “Known”)
You can now use vlookup formula on downlaoded contacts file, by comparing “Associated Company ID” in downloaded conatcts file with “Company ID” in downloaded Companies file. All the matches then can be filtered into a new sheet.
There are plenty vlookup tutorials available online. It seems hard in beginning, but once you are used to it, it works like a charm. Hope this helps.