Recently, I upgraded a user from Outlook 2007 to Outlook 2013. They used Microsoft’s Office 365 exchange service for their email. I set up the account without much of an issue until I got to the autocomplete file. Outlook 2007 stored the autocomplete file as an .NK2 file. Outlook 2013 saves the autocomplete file in a Stream_Autocomplete_***** .DAT file. When you start Microsoft Outlook 2013 for the first time it will try to automatically import your profilename.nk2 file into the new file format. In my situation it didn’t work correctly. It had imported a couple autocomplete files across but not nearly all of them. Here is how I manually imported the .NK2 file from Outlook 2007 into the new Outlook 2013 .Dat file.
Step One: Make sure your .nk2 file is in the following folder: %appdata%\Microsoft\Outlook. Make sure the .nk2 file doesn’t have a .old file (profilename.nk2.old) extension after it. If it has the .old file extension after it delete it.
Step Two: Your .NK2 file must have the same name as your current Outlook 2013 profile to import correctly. To check if the names match:
Click on the Start Menu > Control Panel then click on User Accounts> Mail > Show Profiles. If they match you are ready to go to the next step. If your autocomplete file doesn’t match the name of your profile simply rename it to your current profile name.
Step Three: Click the Start button and then click Run.
Step Four: In the open box, type the following command: outlook.exe /importnk2 and then click OK. This should import the .nk2 file into the Outlook 2013 profile.
I then opened Outlook and all of the autocomplete addresses and contacts were there! I hope this works for you as well.
Source: Microsoft Support Article
This was posted by techspeeder.