I noticed that we can copy files from windows explorer then click paste in the edit menu to add files to Vault folder, but this does not work for design files, dwg, ipt, etc, the paste menu item is greyed out. Why? Is this designed as is?
I would like to add on to Ron's answer a bit. It is definitely recommended that you use the add-ins to add your data to the Vault. The reason being that you want to maintain your file relationships so the Vault can manage them. Adding files directly to Vault Explorer will not achieve this.
Also, the copy/paste command is available from inside the Vault Explorer application. Meaning that you can copy a non-design file from inside VE and paste it in a folder in VE.
For copying files within the explorer client, use the copy design command as this maintains your file relationships.
Hope this helps,
Adam Luttenbacher Sr User Experience Designer Autodesk, Inc.