Smart Converter Pro 3 can be configured to search for subtitles automatically or you can search for them manually. Sometimes you won't get any results though.
To search for the subtitles for you video a unique fingerprint of the file is created. This digital fingerprint is known as a Hash. This is done because you can have many different versions of the same video and if you get the wrong subtitle file it will be out of sync with the video.
If your video is very new then it's likely that no one has submitted a subtitle file yet. If you try again in a few days or even a week you might have better luck.
If your video is a very obscure or not well known then your chances are smaller of finding a subtitle match.
Your language selection will also impact your chances of finding a subtitle match.