It was looking like a "partlogic-0.67" file.
I thought that it was a ".rar" (Winrar zip file).
But finally I found that it is ".iso" file.
Before finding it I was cracked.
Whenever extracted that file it is showing errors.
Finally I find the mystery behind of it.
It is ".iso" file.
I did this:
Open windows explorer.
Open tools menu.
Click on folder options
Then you can see above window.
There you find "Hide extensions for known file types"
Just remove the right option.
Then click on "OK"
Now all files will appear with their extensions.
By this way you can find unknown file extensions.