We can all find nk2edit software which is free and awesome, but here is another method to help understanding…
To import contacts from your old outlook.nk2 file into Exchange 2010 Suggested contacts follow this procedure:
To import .nk2 files into Outlook 2010, follow these steps:
1. Make sure that the .nk2 file is in the following folder:
Note The .nk2 file must have the same name as your current Outlook 2010 profile. By default, the profile name is “Outlook.” To check the profile name, follow these steps:
a. Click Start, and then click Control Panel.
b. Double-click Mail.
c. In the Mail Setup dialog box, click Show Profiles.
2. Click Start, and then click Run.
3. In the Open box, type outlook.exe /importnk2, and then click OK. This should import the .nk2 file into the Outlook 2010 profile.
Note After you import the .nk2 file, the contents of the file are merged into the existing nickname cache that is currently stored in your mailbox.
After the import is finished the .nk2 gets renamed with an . file name extension on the first start of Outlook 2010. Therefore, if you try to re-import the .nk2 file, remove the . file name extension.