How do you archive a Company?
Currently, there isn't a direct way to archive a company in the same manner that you can archive a deal. However, you can achieve a similar action using Custom Fields.
For example, you could create a custom dropdown field that has two options, "active" and "archived," and make all the companies currently in your account "active." You could then set up a filter on the Companies list view page to only show "active" companies. When you want a company to be hidden from that view, you could change it to be "archived."