Steps to register DLL file
1. In your Metro Start Menu, click on the lower left corner and the Start menu pops up. Click on Search.
2. Next, type CMD in the Search App box. Right click on the CMD icon on the left side. Then you will see Advanced on the bottom.
3. Click on the Advanced and select Run as administrator.
4. Now locate the dll file you want to register. cd drive name will change to the directory / folder where your dll file is. dir/w will list the files inside the drive / directory / folder.
5. Next, type regsvr32 [dll file name]. For example – in my screenshot i have registered SelectAll.dll so i typed regsvr32 SelectAll.dll
6. Finally, you will see a message saying registering dll file succeeded. The message would be like DllRegisterServer in [your dll file name] succeeded. That are the complete steps to register dll file on Windows 8.