When you upgrade to Outlook 2010, Outlook 2013 or Outlook 2016, the nk2-file is automatically imported upon starting Outlook for the first time. When you create a new Outlook mail profile or when using Outlook on a new computer, you can import an existing nk2-file in the following way;

1. Copy the nk2-file to the following folder;
   
   C:\Users\%username%\AppData\Roaming\Microsoft\Outlook
   
2. Rename the nk2-file to the name of your mail profile. 
   
   To find out this name use the Mail applet in Control Panel and click on the Show Profiles… button. 
   
   By default, your profile is called “Outlook”. So in that case you would call your file “outlook.nk2”.
   
3. Start Outlook with the /importnk2 switch;
   
• Start-> type; outlook.exe /importnk2
  
4. Outlook will now process the nk2-file and import it into a hidden property of the mailbox but not in the actual Suggested Contacts folder in Outlook 2010 (Outlook 2013 and later no longer use this folder). See the note below if you want to turn them into real contacts. After processing, Outlook will automatically append .old to the nk2-file. So in our example it will now be called; outlook.nk2.old